Game keeps unmarrying my sims

[mememan_w33d420]

So, I have two sims that are half-brother and half-sister, whom I can develop the romantic relationship and get them married. I have the "Allow family" option marked as enabled on MCCC and the Family Relationships Switch ticked in WW. The problem is that whener I boot up the game after closing it, or use CAS, or assume control of another household, they are unmarried when I get back to their household. Any ideas on how I can fix that? A mod that would let me set the relationship between them directly would also help (I tried with MCCC but it doesn't let me add any relationships between them).