In that scenario I would strongly recommend that you NOT file a joint return with your husband. You don't want to be responsible for his tax liability, particularly if there is anything unethical going on.
He is relentlessly uncooperative because he knows that he owes a ton of tax and would rather bury his head in the sand than deal with the issue.
However, unfortunately that does indeed cause a problem as far as FASFA is concerned.
I suggest that you tell him that he needs to pony up for the college tuition since your children won't be able to get any assistance.

