Sounds like OP’s father is not contributing at all so FAFSA-only colleges would only consider their mother’s income but it’s going to really mess kids with a deadbeat wealthy dad who is paying court-enforced child support.
CSS used to (still? @kelsmom ) ask for evidence an applicant wasn’t in contact with their “other” parent (often the dad) - zero contact for years not even a bday card, prison ..
Unless that too has changed, UChicago and Vanderbilt meet financial need based on the custodial parent only (and don’t take the other parent and their potential new spouse into account).