...I suggest you both get into couples counseling immediately.
Legally you can name the child anything you want - but Dad can certainly take you to court to have kiddo's last name changed to his. Hyphenation is more likely if you can't agree (you'd likely be sent to mediation first).
But seriously...are you sure you want to remain married? Because if you can't agree on something like this....you're in for a very, very long 18+ years once the child is born.

