Help with hospital bill

[bingonut]

What is the name of your state? Florida

My ex-husband (still best freinds) was in the hospital 2 years ago while unemployed and had no insurance. They kept him 5 days and ran all kinds of tests and never did find out what was wrong with him. When the bills started coming he applied for some type of assistance from a form the hospital had givin him and was turned down. He paid off all the small bills and made payments on the Drs and Hospital bills. The hospital returned one of his payments asking for payment in full, which of course he didn't have. It was over $20,000. well he called them to ask them to take a lesser amount which he could pay and they refused. It is showing on his credit report as unpaid medical, but has not affected his credit score. 3 months ago he sold his house, bought a used dumptruck (used to make his living) and moved to Michigan. The rest of the money from the sale (about $40,000.00 is in a CD as he explores retirement options) He is renting a room from a freind there and his mail is being sent to my house in Florida. He received a certified letter yesterday that I signed for. It is from an attorneys office in Tennesee. It says that due to your failure to respond to our office regarding this debt (1st time either one of us has gotten anything from them) they have conducted an asset investigation and after recieving documentation from their client will send the account to an attorney in Fl to file suit. It also states that you can call their office today with a visa or mastercard and take care of it. Then it says reciept of this certified letter confirms your knowledge of this outstanding obligation to their client. (I didn't even see the return address when I signed for it and wouldn't have known what it was about if I had) At the end it states that Federal law requires them to tell you that this is an attempt to collect a debt and all information obtained will be used for that purpose. This communication is from a debt collector. Okay... here are the questions.
1. Can they return a partial payment and then demand full payment?
2. Would the suit be filed in Florida where the hospital is or in Michigan where he lives now.
3. Would the money be safe from being siezed in a retirement account? (this is his total savings, he has no other pensions, 401s, IRA's or accounts)
4. Can the money or assets (cars and dumptruck) be siezed if they are in joint names as in mine or his son's and his?

Please answer soon.

Thanks