My fiancé is a saved Catholic and has not been attending the Catholic Church. We together attend a Bible church. We are getting married in June and the issue of his brother as best man has been brought up. His brother will not be the best man unless my fiancé gets a dispensation from the Catholic Church. But in order to get a dispensation, he must promise to raise our children Catholic and I too must promise that. We have decided not to raise our children Catholic. Is there an official way to leave the Catholic Church?
Your fiancé’s brother apparently is working on the assumption that his brother is still a Catholic bound by Catholic marital law. If such were the case, for his marriage to you to be considered valid and sacramental by the Catholic Church, your fiancé would indeed have to obtain dispensations both to marry a non-Catholic and to marry in a non-Catholic ritual (presuming you are marrying in your church). You would not be required to promise to raise your children as Catholics, but you would have to be informed of your fiancé’s obligation to raise his children in the Catholic Church. Your fiancé is the one who would have to promise to do his best to raise the children Catholic.
If your fiancé has joined your non-Catholic church, that is usually considered sufficient indication that he has left his Catholic religion. Because in such an eventuality he would no longer consider himself Catholic or understand his obligation to observe Catholic marital law, the Church would not consider him formally bound to observe the Catholic form of marriage. Assuming that there are no obvious impediments such as a previous marriage or a close blood relationship, and assuming that you too are a baptized Christian, the Church would presume that his marriage to you would be both valid and sacramental.
Although, based on the report you’ve given, the Catholic Church would presume your marriage to be valid and sacramental, your fiancé’s brother may not feel comfortable participating in your wedding party. Whatever decision he makes should be respected. It would also be considerate to your fiancé’s family not to refer to your fiancé as a “saved Catholic.” If he is now a former Catholic, he should be identified either by the denominational name of your Bible church (e.g., Baptist, Presbyterian), as a Christian, or as a non-Catholic Christian. Catholics consider the term saved Catholic, when used in reference to a non-Catholic Protestant Christian, to be offensive to their own Christian faith.
Should I Attend?** by Catholics United for the Faith