Sims in relationship become siblings when adopting a child

Hi!

I had my main sim adopt a child. When the adopted child came home, I had my sims’ partner (they’re both women if that helps) use the adopt interaction with the child as I assumed that would make them both parents of the child on the family tree. However, this made both of my sims in the relationship sisters for some reason. I have tried cas.fulleditmode to set their relationship back to household members which doesn’t work, and my main sims father is now the father of her partner as well on the family tree :’)

I don’t use any mods or CC, I play with them turned off and I’m on PC