I would prefer for my in laws to keep from visiting my daughter for now.
What is your reason for wanting them to keep away?
Because her mother is homophobic, I am not confident that my daughter will be safe with someone like that around her.
You should talk to her about their views and make sure she isn't spreading bad thoughts. You shouldn't keep the  apart though because they are family too.
If she says anything to my daughter, I'm going to report her to the authorities.
It is a good idea to do this if your child is not comfortable being around them. It may be difficult for someone who is homophobic to accept someone who is lesbian/gay. If you fear that your in laws may be overly rude or judgmental than it is perfectly fine to keep them from seeing her.