Since it is a state school, they may not be able to do anything without a FAFSA. If the father can ‘sign’ the FAFSA, even if it is entirely filled out by someone else (and that might be very difficult right now), then they can use that filed FAFSA and appeal it. Most schools have the appeal form on the website, and consider reasons like loss of job or a medical condition or death of a parent, which it would seem both would apply in this case.
It may be that this doesn’t require immediate action. If the father becomes capable of completing the FAFSA some time in the spring, or a court order goes into effect to give someone else POA for the father, the FAFSA can be filed, and appealed, before school starts next fall. If the family has enough money to pay for the school, but the need based aid would help, then it might be worth it to wait and not rush the FAFSA (filing as independent).
If he knows which school he’s going to attend, definitely tell them and ask what they’d need to consider either a professional judgment override for Pell grants, SEOG, or state aid, or their own funds.
I’m glad you are helping him.