Credit and Mortgage...?

Okay my husband and I have been renting for the past year and a half and we feel like we are ready to buy our first home. My husband works full-time and I stay home with our 2 1/2 month old little girl, however I do babysit 4 days a week so I do have some sort of an income. I'm also going to be going back to school to become an LPN starting this January. After checking our credit scores on FreeCreditReport.com, we have come to find that my husband has a horrible credit score (551-570) because of the fact that after his parents got a devoice, his father was ordered to pay one of his student loans but misses his payments very often without my husband's knowledge. However I, on the other hand, have a pretty good credit rating (695). Now if we were to go to a lender, could they go off of my credit score or would they have to go off of my husband's because he's the full-time worker? What is the fluctuation in interest rates for bad credit? Also, is there any way that we can get the student loans under my husband's credit transferred over to his father who has to pay them so we aren't effected by his irresponsibility?