First
I'm not sure where you live, or your age - but I did want to get this out.
Your parents are your parents. If you were raised in a religious household, it's only natural that the parents who taught you about spiritual matters, would be concerned for your soul even when you grow up and move out of the house - even if you're married with your own kids. With them being Catholic, it is quite natural for them to try and welcome you back into that fold.
That being said, only you can decide whether you want to continue in that path or not, and how tactfully you want to place your ball in their court. I must admit my parents and I were under very strained relations when I was attending a messianic congregation while living in their home (though over 18) and it did not get better until I moved out. We now see eye to eye on many things. It just took me moving and them reading and researching afterward for them to change their mind.
Anyhow... as Chava said, you do have to respect your parents. Doesn't mean you have to agree with them or go along with all their plans for your life, it means that you have to treat them justly and respectfully - even if they're the meanest people in the entire world (not that they are) because that is how we are to be to our parents.
I must say I am quite thankful for my inlaws, who are catholic. They are as much family to me as my own naturally born family, and my MIL treats me like her own daughter. They've actually been more understanding about our beliefs than my family who are mostly Baptist/Lutheran background.
While I do disagree with my extended family theologically on many points, I find ways to get out of theological discussions when I know they'll just go sour. There's lots more in our lives going on that can be discussed amicably. I love them to death, and wouldn't give them all away for anything. We actually agree on some things, though we disagree on others. Our theological discussions are less "lively" than those I have with my family back home, because the presupposition that someone must be wrong isn't there. There's an openness and honesty about their questions that I just don't get with some of my family who simply parrot off things they've been told. My MIL will actually investigate what we say, and what positions she holds before making her final decisions.
Try your best to think on the good times, and contact them and let them know your wishes, and try to get together again as a family, even if you are walking different theological walks. It's not good for a family to be so divided and divisive.