The bond between Jacob and Renesmee is far stronger than the bonds of marriage. But I don't see any reason why they wouldn't just make things official. Surely Edward and Bella would want nothing more than to make their Nessie happy...and that would mean allowing her to have Jacob.
I think Tey will get married! It is quite to depressing to think that Jacob will get marreid (I'm team Jacob!) But it ture! He has to marry her. He will love no one eles becasue he has imprinted on her! So they have to get married!!!!