Adopting a child turned the parents into siblings.

After my two sims, who had been married for a while (and obviously not previously related), adopted a child, they no longer had a romantic interaction category. I went to check why that was, and it turns out they were now related. I have McCommand Center and UI cheats and tried to cheat away the relationship in every way possible to no avail. Doing this removed the sibling relationship, but it was promptly replaced by a new cousin relationship. After trying to remove that one as well, it just flip-flopped between the two. I also removed my mods folder to see if it was a mod issue and gave it a try, still didn't work. In CAS, the option to change the relationship was greyed out, despite cas.fulleditmode being turned on. I searched for any solutions, and it turned out this has been a problem for years and it seems the only solution people have found was to delete one parent and add them back with the gallery through CAS. I have spent a lot of time developing these Sims and have no desire to attempt that solution, so please help. I beg.