Apologies up front on an issue that I am certain is a frequent one for you. I am submitting the question, though, as I have not yet found an answer in the Catechism, other books and resources, or in my own heart.
My wife comes from a protestant background - she is the only convert to Catholicism in her family. Her sister is getting married soon and she is marrying a catholic. Here is where the ambiguity beings. He was brought up catholic, went to catholic school, but has not been practicing the faith since living on his own for the past 5 or so years.
My wife and I had a great experience with an Engaged Encounter weekend retreat when we were planning our marriage and so offered to pay for them to attend the retreat as an engagement gift. As it turns out, they have decided to not get married in the catholic church - that is, they are not going to go through any of the preparations required to have the marriage blessed in the church. Instead, they are getting married at my sister-in-law’s protestant church with no intention of practicing the catholic faith.
My question boils down to this:
By participating in this marriage (we have both been asked to be part of the wedding party) - are we encouraging a fellow catholic in the wrong decision? Or is this any different, fundamentally, than a wedding with 2 non-Catholics? On the one hand, it seems to me that by going this route, the groom is essentially declaring that he is leaving the catholic faith and thus he is really already non-catholic. On the other hand, it does not seem likely to me (at least at this time) that he is intentionally leaving to go to another church because he feels a calling to that church. A truer statement would be that neither person is thinking much about religion at all for the wedding or for their future. And I seem to recall that unless someone makes a public declaration that they are leaving the church, then they are just considered fallen away, but we would still act as if they were bound to the church’s rules?
I hope this was not too much information or too confusing - but I feel (fear?) this question has some more general relevance to your audience “What is our obligation (or, worded a little better, our moral duty) when someone raised in the church decides to marry outside the church due to religious indifference?”.
Thanks for considering the question.