For the third installment of his Expendables franchise, Sylvester Stallone not only needed to increase the star power -- adding Mel Gibson, Harrison Ford, Wesley Snipes and Kellan Lutz, for starters – he had to ramp up the action and the stakes.

For that he turned to Creighton Rothenberger and Katrin Benedikt, the husband-and-wife screenwriting team behind Olympus Has Fallen and its upcoming sequel London Has Fallen.

In The Expendables 3, in theaters now, the mercenaries face off against Conrad Stonebanks (Gibson), the group’s co-founder turned corrupt arms dealer. With big targets on their backs, the veterans recruit a group of hot young guns to join the fight and potentially give them the upper hand.

SPINOFF spoke with Rothenberger and Benedikt about collaborating with Stallone, the challenges they faced in juggling 16 major characters, their plans for London Has Fallen, and more.

Spinoff Online: How did you become attached to The Expendables 3?

Creighton Rothenberger: After Olympus Has Fallen, our reps came to us and asked us if we would like to throw our hat in the ring for Expendables 3. Katrin and I looked at each other and said, “Chance to possibly work with Sylvester Stallone? Absolutely.” They put us up for the job, we had to come up with our take for the movie. We probably pitched it to the studio three times. Then we made it to meeting Sylvester Stallone. We drove up to his house in the Hollywood Hills. Producers Avi Lerner and Boaz Davidson were there. We pitched our idea, the meeting went well, Sly was very professional and then we left.

We heard two weeks later that we had made it to the final two or three writers. We went back, and that time was just Katrin and me and Sly. We sat around talking about the movie for an hour or so. We left and the next day we got a call from the studio saying he had picked us to write it.

Katrin Benedikt: It was over the course of a lot months. Sly is a busy, busy guy. He has so much going on. When we met him that last time, he kind of said, “I have a story I’m thinking about.” We went, “OK.”

We just all collaborated and gave our take on that story and went from there.

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Where did the idea for these young mercenaries develop from? What were some of the goals for this installment?

Rothenberger: That was Sly’s idea for the young Expendables, so we ran with that. The Expendables is a template to a certain extent, but you are also given leeway. Things are also constantly changing. Our goal was to try to make it bigger and different and, if possible, better than the two previous ones, which had done very well at the box office.

Benedikt: The goal was just to make it as fun and fresh as possible. You really want people to go and have a good time.

Rothenberger: The Expendables movies are fun rides. You have these icons from the ‘80s and ‘90s that are all getting together. I think if you had said to anyone in the ‘80s, “OK, we’re going to have a movie that has Harrison Ford, Arnold Schwarzenegger, Sylvester Stallone and Mel Gibson, all in the same movie,” you would have gotten, “That’s insane and will never happen.” They’ve done it, and it’s just a fun roller-coaster ride. You want to entertain the audience as best you can.

Cast changes cause script changes. Bruce Willis was originally signed on to reprise his role of Church before negotiations fell through. In what way did that alter your game plan?

Rothenberger: We had to create the Drummer character, which was Harrison Ford. We originally wrote Willis’ Church character into number three. When that changed and Harrison Ford came on board, we had to create this new character for him. It’s awesome being able to write for Han Solo.

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How challenging was it juggling the older characters, introducing the newer ones, and giving them all unique voices and individual moments to shine?

Benedikt: That was probably the biggest challenge in writing Expendables 3. You only have a little over two hours.

Rothenberger: There are 16 major characters and you have about a two-hour run time. To try and give them all their moments to shine, that’s probably the most challenging part, just because there’s so many roles and so many parts. Then you throw into that the scheduling issues and how much time someone has on set … There’s all kinds of things that the viewer and the audience isn’t privy to that you have to take into account when you’re putting the movie together.

How did you approach the action for Expendables 3 differently than Olympus Has Fallen?

Rothenberger: The action from Olympus Has Fallen, even though some of it was definitely out there, it all started with trying to be as grounded as possible. Obviously, there’s going to be that craziness you expect out of a movie, but we wanted it to be as grounded as possible. We did a lot of research in terms of what could happen, and if it could happen, how would it most likely happen. We kind of take it from there.

With Olympus, there were ex-Secret Service agents that were on set. They really kept us in check regarding what would actually happen, what could actually happen and we tried to make it as real as possible. They told us that what we came up with was grounded and real and could conceivably happen.

With The Expendables 3, it’s more like anything goes, to a certain extent. It’s more popcorn. It doesn’t have to be as grounded. You have a little more leeway. You could do stunts. You wouldn’t have crazy stunts necessarily in Olympus Has Fallen. In Expendables, the audience expects that.

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Did you take into consideration any of the actors’ strengths when conceiving those action sequences?

Benedikt: Yeah, definitely. Everyone has their own strengths. Some guys are big and physical. Other people, like Antonia Banderas, are more lithe and will fight in an entirely different way than someone else. We tried to make all the characters distinct in the ways they fight and battle their enemies. That was a fun thing to do, to have all kinds of different fighting styles. Ronda Rousey fights one particular way. We were helped immeasurably with a phenomenal fight choreographer and stunt guys on set. That added a lot to the movie.

Rothenberger: The characters we created, like Victor Ortiz’s character Mars, is a weapons expert. Again, you write as much as you can into the script, but you may not get to showcase all of it. You’re limited to a two-hour movie. Ronda’s fighting skills were obviously a highlight. Kellan Lutz we had with the motorcycles, with an almost X Games stunt aspect to it. Those were the types of things we really tried to focus on, to bring something new and different that hadn’t really been seen from the older Expendables.

How much fun was it writing dialogue where you get to give a wink and nod to the actors’ prior projects?

Rothenberger: That was a lot of fun because you have all these iconic stars. How often does a writer get the chance to write lines for Rocky and the Terminator and Indiana Jones and Mad Max and Blade and Zorro and the Transporter, all in the same movie? That just doesn’t happen every day. It was a great opportunity and really a pleasure to write for all those guys.

Sylvester Stallone is known for improvising and changing things up. Since you were on set, how collaborative was the environment?

Benedikt: It was very collaborative. It was a great set. Everybody got along. It was really a terrific collaboration with everybody. You would think with all these stars … but, no. It was a terrific set.

Rothenberger: Katrin and I were on set writing for eight weeks. It was a very busy time. We were certainly constantly doing something, but it was a blast. It was a phenomenal experience.

Have you set up Expendables 4? It almost feels like you are ushering out the old guard and bringing in the new.

Rothenberger: The studio is really just in the preliminary stages for 4. We, as writers, haven’t gone down that road.

Benedikt: The bottom line is this is Sylvester Stallone’s franchise. I’m sure he probably has a vision on how to keep it going. He’s the glue that holds it all together.

It was a great idea to take all these icons, put them together and have them in a cool, action extravaganza. You would never expect all these guys in the same movie at one time. I’m sure people in other genres, or with other genders, are going to want to try the same thing.

Looking forward, the sequel to Olympus Has Fallen, London Has Fallen, is due out in 2015. Can you talk about the premise, and how it differs from the first one?

Rothenberger: This one takes place in Europe. When you’re doing a sequel, you try to top the first one. Instead of our character, Mike Banning, trying to protect the president in the White House, now it’s going to be taking place in London, where all the world leaders are gathered for the funeral of the British Prime Minister. Bigger stakes. In essence, the most-protected event in the world is now the target. So, what happens?

We delivered our first draft of the script to the studio, and now it’s really in the studio’s and stars’ hands. We saw they have a release date for October 2015. As for when they start shooting and all those details, that’s all in their hands right now.

How do you go about making it bigger and better besides switching locations?

Benedikt: It’s very difficult because so much has been done before. You’re trying to be original, different and interesting. You’re trying to think, “If I was going to do something evil in this world, what would I do?” It’s really about trying to evolve and progress your characters in terms of where they are going. Also, you create a bigger canvas for action.

Rothenberger: While there may be nothing new under the sun, on another level, you can put it together in ways that you might not have seen before. With our original idea for Olympus Has Fallen, we thought here you have a Secret Service agent in his prime, protecting the president. That’s a pretty big platform that could travel anywhere in the world.

Benedikt: We always hoped it would become its own franchise, and hopefully it will. It has big stakes and a cool hero. Gerard Butler, Aaron Eckhart and Morgan Freeman are awesome. We had very good fortune with the casting of our first movie, Olympus. Like with Expendables, we’re trying to keep the train rolling. Try to make it bigger. Try to make it better. Try to expand it and if there is still a hunger for these characters and for these adventures, to try and satisfy that hunger.

There’s a balance of wanting to create bigger and better and more interesting. At the same time, there are certain reasons that people love to come to an Expendables film or to go see an Olympus Has Fallen sequel. There are certain expectations from your fanbase. You want to make sure that you deliver on that.

You also have a supernatural action thriller in the pipeline. What’s it about and any update on its status?

Rothenberger: We’re pretty close to finishing it. We’re actually pitching it as Chronicle meets Wanted. We’re sort of keeping the actual logline under wraps for now. It has a really cool central idea that we think audiences will like.

Lastly, with Expendables 3 and Olympus Has Fallen on your resume, would Gerard Butler make a good addition for Expendables 4?

Benedikt: Gerry Butler is such a talented actor and definitely, without question, an action star. He can basically do whatever he wants. I could totally see him in an Expendables movies. He’s very versatile.