How should I handle some people in my family who are upset about our wedding ceremony because they're Catholic?

As sons and daughters, we have an inherit need to please our parents and make them proud of us, but as husbands and wives, we have the responsibility to always have our partner's back and to stand up for them regardless of the person causing the conflict. If there is one thing I have learned from life in general, it's that trying to please everyone only leaves you empty and unhappy. My advice would be to speak to your families and explain to them that you really love your partner regardless of his or her religion because the most important thing is how he or she makes you feel. The wedding itself is just a symbolic representation of the bond you two are forming, and that's what they should be focused on.