Re: Divorce then marriage

If your Sims are married, I'm not 100% sure they need to divorce. But you can achieve a divorce by doing some mean actions between these Sims. 

You can always have another romantic story next to the current one. Your playable Sims sound be able to get married. 
If you still take care of the little pink events that pop up for the kids they should just grow up all happy and with a good upbringing. 

You kids will still be in your house, you can have kids interact with each other and they should get labelled as 'half-brother/sister'.
Which would mean they can't have a romantic relationship.