Cannot set parents for pre-existing sims

Checked the list to see if this was already reported, but wasn't seeing it. Sorry if this has already been posted.  

Recently was gifted R&L, so I've been going through and retroactively building some families up a bit. I wanted to add grandparents to a household that previously didn't have grandparents. Two of the sims are sisters and I generated sims via genetics--the dad from one sister, the mom from the other. Once I had done this, I could NOT assign the mother to the other sister and vice versa with the father. They didn't have the full list of relationships available. I moved the grandparents out, saved them separately to the gallery/library and deleted them, then re-added them to the household to attempt fixing their relationships that way. This did not help and, in fact, made the issue worse. Both grandparents CAN be one of the sister's husband's parents though (and could be when I'd first made them as well).

Father is correctly assigned to this sim, but there is no option for her mother to be anything other than a Household Member or Partner. After moving the parents out, saving them to the Gallery, and adding them back in, the mother could be a sister or partner, but not a mother.

Father assigned correctly to one daughter, but cannot be assigned to the other.

Same as above, but inverted.

 No Mods/CC. PC. EA App. 

Let me know if there's anymore information needed for this.