Let me tell you some things you may need to know, not necessarily in order of importance.
1. I am not an attorney and can't give "advice". My suggestions are based on general principles as I do not have specific facts about your situation.
2. I would not file a joint return with your spouse until you have everything else straightened out. Filing a joint return can make you jointly responsible for his problems. I would also not hold any joint bank accounts or joint credit cards, or buy any property together, unless an accountant reviews his information for the last 8 years and tells you it's OK.
3. Married spouses always have the choice of filing jointly or separately. A joint return lists all the couple's income and deductions on one tax return. With married filing separately, you each file a separate return listing only your own income and deductions. You must include your spouse's name and SSN but not their income information. (A spouse's income may be asked to determine eligibility for ACA credits but is not part of your tax return.)
Married filing separately usually results in higher taxes owed and smaller refunds, because many deductions and credits are limited or disallowed. But in your case, I would not file jointly unless an experienced accountant who has reviewed all the details of your situation gives you the OK.
4. A person may not be required to file a return if their income is lower than a certain amount or if their income is from non-taxable sources, like SSI or SSDI. If a person is required to file a tax return and would be owed a refund, there is no penalty for not filing or filing late, but the refund won't be paid. If a person does not file and owes tax, penalties and interest start to add up quickly; 5% per month for the first 5 months then 1% per month after that. And, the IRS has up to 6 years after you file to audit you for a particular year. If you never file, they can audit you forever.
If your spouse works a W-2 job and has income tax withholding, and doesn't file, the IRS creates a substitute tax return in their computer system using the W-2 information. But they don't give credit for any deductions or credits or dependents unless the taxpayer files and claims them in writing. If the substitute tax return shows a refund the IRS will not pay it. If it shows tax due, they will definitely send a bill. If your spouse works for cash, the IRS may never know about it unless something happens to make them decide to audit him. In that case, they can go through his bank records and declare that any money he received, and any money he spent on himself (cars, houses, clothing, etc.) was work income, and subject to tax and penalties, unless he can prove it was not work income.
5. I suggest you see an accountant, especially an enrolled agent, to determine if your spouse was required to file, to prepare the correct tax returns, and to try and negotiate a settlement with the IRS that may reduce the tax he owes. Until then, I would be extremely cautious about making any joint financial arrangements or entanglements.
