Legal Question in Family Law in Maryland

Re: Father of child unknown, can I put stepfather on brith certificate?

Your husband can file a petition for adoption, but you'll have to make a good faith effort to put the bio father on notice of the petition so he has a chance to participate if he objects, even though that's highly unlikely (I assume when you said the bio father is "unknown", you were referring to his whereabouts.) This means sending the papers to his last known address and probably placing an ad in the newspaper. You should check with adoption support groups in the area or do some googling for further information.