I think the question you really need to ask yourself is, “How do we want to raise our children?” Have you and your wife decided to raise your kids as Jews? Catholics? Both? This is a conversation that needs to happen before you give your in-laws direction.
Once you and your spouse establish a “game plan” for the cultural and religious identities of your children, then you can give your wife’s parents some guidance as to what’s acceptable to you and what isn’t. If, for instance, you want to raise your children with a strong Jewish identity, then you can do things like send them to a Jewish religious school or celebrate Jewish holidays. If the kids are secure enough in their Jewish identities, then a few Catholic influences probably won’t disrupt their Jewish-ness.
In addition, remember that your wife’s culture is important to her. It can be enriching for your children to “help” her and your in-laws celebrate their Catholicism. Think of “helping” a friend celebrate her birthday. It’s not your birthday, but you can certainly go to the party, eat cake, sing “Happy Birthday, and take home a goodie bag.
Whatever you decide, be sure that you and your wife communicate it clearly to her parents. I wouldn’t “cry foul,” so much as let them know how you and your spouse have decided to raise your children. Moreover, let your in-laws know that you’d like them to be a part of their grandkids’ lives, and what they can do to help.
Jim Keen is the author of “Inside Intermarriage: A Christian Partner’s Perspective on Raising a Jewish Family.” He has been in an interfaith relationship for 28 years, and has been an active participant with his wife in raising their two Jewish daughters. They live in Ann Arbor, Michigan where Jim teaches in the Ann Arbor Public Schools.