How to remove hidden sibling family relationship between gay couple sims?

I have a save file from 1-2 years ago featuring a male gay couple who adopted a daughter. Recently, when I resumed playing this save, one of the Sims was abducted by aliens and returned with an alien baby.

The problem emerged when both Sims started getting "Fear of Being Cheated On" moodlets, requiring romantic interactions to overcome. However, I discovered they couldn't perform any romantic interactions except "Comfort Over Shoulder", despite having full romance bars.

After some online research, a player suggested checking family relationships. In CAS they show as spouses, but the alien baby refers to her non-biological father (stepfather) as "Uncle", and vice versa. Using MCCC mod, I confirmed there's an unintended sibling relationship between the couple, explaining why the alien baby and her stepfather has niece/uncle dynamics.

I've tried removing the relationship through cheats but failed. I used MCCC to modify their relationships. While I was able to remove the brother relationship at that moment, two issues persisted: firstly, there were still no romantic interactions available between them, and secondly, upon checking in CAS, they still maintained the niece-uncle relationship dynamic.

I also attempted to upload these Sims individually to the Gallery and then reassemble them into a household. However, this approach resulted in the loss of all their non-family relationships, which is not what I intended.‌

Does anyone know a way to remove this hidden sibling relationship without resetting their other social connections? Any mod/cheat solutions would be greatly appreciated!

PLUS: I just discovered that both the identities of sibling and spouse can be viewed in Genealogy at the same time.