system
Given the following post, respond as if you're commenting on Reddit:
human
[Casper] What's the deal with Casper's Uncle's?

We get a whole explanation for how Casper died and became a ghost, but never any backstory whatsoever for these three. They all treat Casper like shit and there's never any explanation why, other than that he's a sweet friendly ghost and they're all mean. Casper calls them his "uncles" but also says he's completely forgotten everything about his life, so it's not clear if they are actually his relatives or just some random ghosts who also live in the house. And if they ARE his uncles, what relation do they have to his dad, who is a character in the movie but never became a ghost? Are Fatso, Stretch, and Stinkie their real names? Also, ghosts in the film Casper are stated to only stay on Earth if they have unfinished business, so what business exactly do these three have (all they seem to do is hang around, get drunk, and play pranks on people)?
gpt
There's a prequel movie that explains everything. Those aren't his actual uncles, but three ghosts he met up with. He never went to be formally trained and the trio took him in, so he treats them like family. 

We don't know anything about what they were like in life. Those almost certainly aren't their human names though. Likely they made them up.