Is it my parent's house or my parents' house? Except for a child custody matter, where one parent's rights might be called into question, I am going to say that we use this word in the plural. We don't really talk of one parent as in "I am going to see my parent tonight" or "My parent is in the hospital." So let's go with plural possessive.
...We spent the evening at my parents' house.
...My parents' best friends were over.
Happy punctuating!
Margie