^^ Vampires' regeneration is based on the base form of the individual. The normal size of their fangs is set, and the magic simply recreates it as it were before being damaged.
^ Also, they are there for puncturing the skin in most cases, only more a few types of vampires have straw like fangs, like Marceline the vampire queen.
PineconeJuice They got "married" in the first episode and in the last were shown to be wearing wedding rings. Show Director also said in an interview attached to the blue ray they were married.
^ "Good thing I have these drinks ready on hand. Gotta slake this thirst you are stirring in me. Feel free to take hydrating break every now and then too."