What is wrong with this household?

I think I figured it out. I went back into the game yesterday and removed all preferences tied to romance for both Sims. However, they were unable to interact romantically with each other afterwards - no flirting, no physical interactions other than offering a massage, nothing. Both were still in a flirty mood, though, and when I checked their social contacts, they both were listed as romantic partners for the other one. For some reason, I clicked on "show profile"... and that's when I saw that for some reason or other, the game considered them to be siblings AND spouses. There was no way to change this in CAS, so I quit the game without saving, then went back in. Only one of them was labeled "sister" for the other, and only in CAS. The second I removed the romance-related dialogue options, both profile cards flagged them as siblings. Deleting the second spouse from the world didn't do anything to change that, either.

Now I haven't dealt with resetting their relationship yet, but I suspect that the "sister"-label may have been there from the day I created them. It would explain why they have been behaving erratically from the start. For all I know, I accidentally clicked "sibling" for one of them in CAS and "spouse" for the other one, then saved them both without making sure I had chosen the correct options. Or maybe it's just that infamous sibling bug.

Either way, I was unable to remove the sibling bit via CAS, or cheats, and since I don't want to use the workaround where I save one of them to the library, then delete her from the household, re-download her, and fix all her relationships, I've now installed MCCC to get rid of the sibling label. Once that's done, I'll move that household to the bottom of my priority list and only play them for a bit when I feel like it. I was running out of ideas on what to do with them anyway, so in terms of gameplay and storytelling, paying them less attention won't be such a big deal.