Marriage for RP only, with the religion system, would be fine. The only advantage I would consider would be the option to say 'We're pregnant!' and 9 months later you have an economic drain in your house that you have to feed... but after a few years it (the child) can perform some very basic tasks at a low level. That's really more effort than it is worth, though.
So yeah, that brings us back to RP only.