Casper the Friendly Ghost is one of animation's oldest characters. The story follows a young ghost who chooses to make friends with the living rather than scare them. However, this is often met with negative feelings from his caregivers, the Ghostly Trio. Over the decades, it was never addressed whether or not the trio was related to Casper, but the 1995 family film of the same name confirmed exactly how the older apparitions are connected to the young ghost. But the confirmation of their common lineage still leaves a few questions instead of answers.
In Casper, the Ghostly Trio consists of Stretch, Stinkie and Fatso. Stretch is the ringleader of the three and loves to order his brothers around. Stinky doesn't mind taking orders, as he takes joy in scaring the living with his ghostly bad breath. Fatso acts as the least intelligent of the bunch, and even after his death, he still can't get enough food. The three take their scaring seriously but don't care to make their afterlife any tidier than when they were alive. As a result, Casper constantly cleans up after them, and in a poor trade-off, they treat him as a slave.
Casper does an excellent job at giving audiences a brief look at the character's long-running history in the opening minutes. The group of ghosts that reside in Whipstaff Manor manage to scare off every living thing that tries to exorcise them, except for the father/daughter duo of James and Kat Harvey. The trio learns to tolerate humans a bit more while Casper develops a close bond with Kat. Through Kat learning about her new friend and a deleted scene, the film also confirms that the Ghostly Trio is, in fact, Casper's blood-related uncles.
The scene takes viewers into the attic, where audiences learn of Casper's father, J.T. McFadden. Following the young boy's death due to pneumonia, J.T. was obsessed with inventing a machine that could bring the dead back to life. However, he was admitted to an asylum and never got to see his work completed. Ever since then, Casper and his uncles have haunted the halls of Whipstaff Manor. While the scene confirms their relation, the exact connection between the trio and J.T. is never explained. That being said, they may be his brothers, as they still care about Casper even though they're mean to him.
Another detail that is left unknown is the Ghostly Trio's exact cause of death. They may have died either in the same instance or close together since their bond is so strong. It's also possible they died sometime after Casper and chose to watch over him while they have their own fun scaring people, so he isn't left alone. In conjunction, Casper most likely helped them cope with their own deaths, never condemning their desire to scare people as a result.
The core theme in Casper is about family and loving them even after they've passed away. However, Casper takes on this idea in a more literal sense. Making the Ghostly Trio related to Casper only bolsters this notion, showing unconditional love at its finest. While they're often mean to Casper and berate him for caring about humans, they still care for him deep down. In the past, there was no clear explanation for why they stayed with Casper, but now it's clear that it's because no matter what, family supports one another.