My in-laws are germ freaks and they are insulting people when they come to see their 7-month-old grandchild. They want everyone to use hand sanitizer before touching her, and they complain about any animals that she can possibly come in contact with or anyone who owns animals. They act as if everyone and everything is too dirty for their grandchild. How much exposure to germs is ok?
It's always a good idea to be aware of how germs spread and how to limit that spread with your baby. But one thing is certain: You won't be able to change their minds about their parenting style. The best thing to do is smile and nod at their good intentions and then do your own thing when your in-laws go back home. Just remember that and try not to get too frustrated.
Many parents have walked in your shoes, having to deal with the joys and challenges of having their own parents around to help take care of the kids. Most of your friends won't be offended by the comments, since they may have had the same experience with their own in-laws!