I think that legal marriages should exist, but between same species only...at this point. But contracts would definitly be the way to go. Then the individuals involved can choose whether they want some kind of ceremony as well. A legal marriage is basically just that anyway, a contract. If you get married by a judge, no religion (should) has it's say in your union unless you allow it.
Life is about the journey and not the destination,
so what better way to know life
than to wander all the roads and paths set before you.