How can I fix my immigration status? what options do I have?

My boyfriend is Cuban and he came to the U.S. through the marriage of his Dad with an U.S. citizen. When he came into the country he was given a conditional residency for two years, but his Dad failed to file for the i751 to remove the conditions and receive the 10 years permanent residency. As a minor he was completely unaware of the situation so now when he recently found out about his case he filed the i751 attached with a letter explaining why his Dad never took her of this issue. He just received a notice asking for more proof of the marriage like pictures, taxes, leases, bank accounts that his Dad and stepmom have together, which he has. The problem is that they are divorced now, but when the form was supposed to be filed they were married. What can he do to solve this issue? does it matter they are divorced now? should he get a lawyer? can he face been deported even been Cuban? or should he just file a new form since his Dad is a Citizen now and he could claim him?