[ARCHIVED] Parents have romantic interest in their children

That's an interesting problem. It's definitely a bug and not a "feature" of some mod. None of the romance-related mods allow that, it's understandably banned by every mod I've ever seen.

I'm not sure it's possible to completely remove it from the active sims.

The easiest way would be to save the household to your library, delete the household from your active game, and re-insert them from your library.

That'll very likely reset the entire household. Problem with doing it that way is you'll lose all relationships and likely career status as well.