Marriage is not manditory for any character by chapter 11. If you choose to let certain characters marry later on it will only open other bonus levels with the child (composed of skills based on their parents). This can happen in the last chapter if you really want it to, and timing is no real issue. You don't have to worry about forcing units together cause they're support will grow through the game and you can end up with these alternative chapters much later.
Has anyone else updated their wireless feature in the game and found about 10 characters from old games with teams that you can fight and recruit? Just saying might want hit that little up date button and vs Eliwood, or Hector.