Marty doesn't need to have money for his kids to go through college. There are loans, scholarships, and work study available to put anyone willing to study through college. Maybe in the 50's only one child could be put through college, but now anyone can do it because it is not dependent on parents anymore.
I have to say I am baffled that the girls keep asking if the women would pay off their loans. The girls have graduated, and they should be fully able to pay off their own loans, it is not their parents duty to pay them. I am hoping that they are asking the question only to find out who is truthful enough and has the spine to tell them to pay their own loans. Kind of a trap question, they are hopefully hoping for a "no" for that question, and so far the women have passed. If the girls are hoping for "yes", then all I have to say is .