Hello,
I would like to know how common are these kind of contracts? Are they legal and will my bank work with the person who is interested in doing this contract?
It is always best to at least consult with an Attorney, most offer a free first consultation so there is no risk on your part. Laws are constantly being changed or updated and they may know something nobody else has found yet. It seems almost everyone is a "legal expert" these days but it's always best to get advice from a licensed Attorney and even one that is Board Certified in the specific area you are having issues with. They will know the questions to ask that will give them the full scope of the issue/problem. Get as many free consultations from as many Attorneys you can find until you feel confident you have found the right one for your situation.