Intentionally filing using the wrong status is illegal and could be considered tax fraud/evasion. However, your situation seems a little different. You both should have filed a joint return or married filing separately. Since he filed a separate return which you were not on, you should have no liability. If something does arise, you should look into innocent spouse relief.
If you received a 1099, then your "employer" considers you an independent contractor and the payroll taxes are your responsibility. You will have to file a schedule c with your return to show the income and a schedule se to compute the self employment tax.
I certainly understand the family concerns. What you are contemplating is not actually a donation. A donation is the giving of one thing to a person without anything in return. If you want to include the rent paid as the reason for the transfer, then you should consider an Act of Sale, especially if you are to continue making payments.
Take the market value of the home and include that many past payments as the consideration.
It sounds like your husband abandoned the household. There are exceptions to the general laws when this happens. Greg Rome is a local attorney in Chalmette who is a young expert on Louisiana law. I would contact him. His firm is Williams & Rome on Pakenham.
There is no time limit in the sense that an executor only has 6 months or 1 year (because if a will is found it can be probated anytime). If there are problems, then you should contact an attorney. Under Louisiana law, a person technically takes ownership of an item upon the other person's death. However, the recipient may not have possession, which seems to be your problem. The solution to this is finding an attorney, telling them there is a will, who has it, and where. The attorney can...