Partnered Sims turn into siblings

While playing a new save the family tree made a mistake of the relationships twice.

 Sim A (very first sim made in this save) had a baby with the grim reaper, married another sim and had several children, then had a secret child with the grim reaper while married. When I switched to another household, the secret child's true father was discovered (I'm assuming), and the family tree then listed the grim reaper as the brother to Sim A's husband. The family tree shows both the grim reaper and Sim A's husband have the same "unknown" parents. Thus the 2 children Sim A had with the grim reaper were then listed as niece and nephew to Sim A's husband instead of stepson/daughter. 

The second error occurred in the same save file when Sim A married Enzo Alto after the previous husband's death. After marrying Enzo and moving in with him, Enzo adopted one of Sim A's children. After the child was adopted, the family tree showed Enzo and Sim A's husband as the child's father, and Sim A as Enzo's sister due to the same "unknown" parents. Now Enzo and Sim A are married siblings (while Sim A's child is now listed as her niece), making the married couple unable to have any romantic interactions although they still have a romantic relationship bar + dynamic (screenshots below). My game is up to date, I am not using any mods, & the option to change their relationship in CAS using cheats is grayed out.