Again, thank you to everyone who has replied.
I’m guessing the psychiatrists will advise against bringing up the FAFSA with my uncle right now, since while he’d be capable of understanding it and signing, he shuts down at anything that causes him stress. While this is by far the most severe mental health crisis he has had, it isn’t his first, and every time, the trigger was related to finances.
The psychiatrist does think he is stable enough and would be willing to sign a power of attorney, although we have to wait for a formal evaluation. Until then, while there were enough documents around the house that we have a pretty good picture of the finances, we probably don’t have everything needed for the FAFSA quite yet.
I did find a special circumstances form on the university website, and it looks like he’d fall under multiple categories in which reconsideration is granted.