Partnered Sims turn into siblings

My engaged gay couple suddenly became brothers. The one who isn't supposed to be part of my family tree (Harry) suddenly is, their adopted daughter now has a "niece" relationship to the other one of the dads (Eddie), who was originally in my large family tree, they cannot have romantic relations. I felt like this happened after Harry also adopted their daughter - she was first adopted by Eddie via phone, but something else could have caused this. The relationships are not editable in CAS, the guys still show up as engaged in there with steamy dynamic and even though the option of "household member" is not greyed out, I cannot choose it, it reverts back to engaged. I cannot change the relationship with their daughter either, even with fulleditmode on, it says I cannot edit pre-existing sims.