(I know it's highly unlikely, culturally, for two people to be living together apart from their families before marriage, but it's for a fic I'm writing, so let's pretend that all the living together and vow of being together forever stuff is taken care of and all they have to worry about now is the "marriage" part. Also, having a ceremony isn't practical, since they're on their own with no family or friends nearby to celebrate with. What do they have to do to make the marriage thing official when everything else is taken care of already?)