Would use both with a hyphen. That will be on he BC and SSN. I know people arent going to spell her whole name so im not worried :)

Baby should have dads last name if he is a part of the babies life regaurdless of marriage or not in my opinion. My boyfriend and i are obviously not marries and while someday we will get married its just not a priority right now. There is no question our daughter will have his name.