I made my own fraternity house, and gave each of the 8 bedrooms a double bed. Since the empty housing attracts a full roster of roommates from available townie/student sims, it's a random mix every time.
And what I found out is that if a married townie gets drafted as a housemate by the game's roommate allocation algorithm, then his wife will move in as well. So we had a woman - and a 9th resident - living in our fraternity my sim's last term at Uni.
Possible to occur, not possible to arrange deliberately.