asPapi, you should know that there is no conditional card in a case when a USC child petitions a parent.
Definitely, his dad is married and his GC is conditional.
Do you have a joint lease/mortgage? do you have insurances in both names? did your father name his wife as his beneficiary on his life insurance? and vice versa? Can you get more bills with both names on it? do you have pictures of outings together? affidavits from friends and family that it is a bona fide marriage? Do you mean to say that in two years they have gotten NOTHING JOINT? joint taxes, credit cards, adoption papers for a dog/cat, pics from vacations they took together? can their priest/pastor/etc. testify that they go to church together and participate in church activities together?
And remember - never ever send originals.