Adelaide_Astraea
I might have found a solution to this by talking to a modder (Tyjkor! THANKSSS!!) who told me that it looks like the issues were caused by the "Poor Leadership" relationship bit. Basically, you have to edit the relbit off of the characters to stop the bad behavior. I have played all day and NO BAD MOODS! No anger at all! It seems like this relbit got added to everyone in my household. I am not entirely sure if it's EVERYONE or not I haven't yet checked--I was just TOOOO happy to have my precious sisters back to normal again!
I used MCCC to remove the relbit from the sisters (and assume it would work to remove it from anyone else it got added to!) I am not sure if there's a specific cheat to remove this relbit or not but it was super easy with MCCC. (I hope it's okay to give instructions here--if not please remove them mods!)
--ensure testing cheats are on
--make your Queen your active sim
--click on your Queen's husband (King)
--open the MCCC menu
--scroll down to the bottom to "Relationships" and click to the next menu
--scroll down to the bottom to "Relationship Bits" and click to the next menu
--click "Remove Relationship Bit"
--scroll through the bits to find the one that is from the Royalty and Legacy expansion--it should reference something about "poor leadership"
--click it to remove it
After that you should be able to close the windows and your sims relationship should return to normal. Not gonna lie, I did edit a few of the other relbits from the negative behavior out too so that it was like resetting them to their original friendship/relationship dynamics without any hurt past feelings. (I used cheats to remove the negative milestones and such too lol I just couldn't handle my babies being so mean to each other!)
I hope this helps you get your precious Queen and King back to their loving selves! <3
(PS I did NOT find any relbits that would remotely explain the horrifying act of becoming flirty with your family members thus far. Thinking it's a different issue than this one all together!)