Depending on the state you live in you should be able to marry. As for the legal father thing as long as you both sign the birth certificate you are the childs legal guardians. The hospital may require documentation as to the sperm if you don't have any documentation say you did it all at home, you can always get a dna test to prove the transgender as the father. All they have to do is take a swab sample of saliva from the mother, child and father.
