Family Tree Glitch: The Sister No One Asked For

I had the same thing happen to me. My sim self's daughter's ex-husband often finds himself as the brother of her current husband and this is often corrected via MCCC. I had to delete my aunt and create her from scratch again as she kept becoming the brother of my father (who is still married to my mother in game!) I couldn't correct this one with MCCC so that's why i had to delete her.