It is enough that you informed them that this debt was fully paid and provided proof. I have no idea why they needed you to wait until Friday.
If they continue to contact you, this will be a great FDCPA case. File a suit against them.
The fact that you did not sign a quit claim only affects your rights as to all other individuals. Your contract affects your rights against your co-signor. As an example, if somebody sues you for your interest in your property, they are not bound by your contract and they can seek to have your interests liquidated to their benefit. You (or your co-signor) cannot use that contract as a defense against others. However, between the two of you, your contract will be enforceable (arguably).
Have you at least consulted with a BK attorney? I don't think you should look to it as a "last" resort. It seems like it would cure everything much more easily than what you are going through now. Very often, people are surprised at how easily a bankruptcy can be done and solve their problems.
If you are the sole individual on the deed, there is no need for a quit claim deed (it only transfers interest in property).
You main problem is that a spouse may be entitled to 50% of the property if it is a marital asset. Was this purchased/acquired during marriage? Were payments and maintenance costs paid from a joint account?
If you are unemployed, there is no question that you should consider a bankruptcy. In your case, you have to make sure the $100k is a dischargeable debt. Its a pretty easy question to answer, make sure to contact an attorney and get a free consultation instead of complicating things with this lawsuit. Good Luck!
What is your foreclosure defense based on? Some of the "popular" defenses you hear about on the news have already been determined (unfavorably) in Maryland. Also, since you have been fighting to keep your house, there are other options, such as restructuring in bankruptcy etc. Any attorney will want money upfront and hourly. Foreclosure defense isn't something suitable for equity share arrangements.