Does his wife belong to a church that celebrates the traditional Latin Mass?
I’m asking questions because I’m trying to solve the mystery here. :-) Many Catholics in my family married Protestants, and I have personal experience myself.
Here’s what I learned personally through the Catholic Church:
The Catholic Church recognizes marriages between Catholics married in the Catholic Church, Protestants married in Protestant churches, and Catholics married to Protestants when the marriage is blessed by the Catholic Church. The blessing is some paperwork and exchanged vows. No big wedding is required. (For Catholics married to non-Christians, the process is more complicated.)
So, I’m thinking one of two scenarios must be true: Either (1) someone misled your brother into believing he had to convert and have a wedding, or (2) your brother knows he did not have to convert or have a wedding, but he’s telling you that he had to. :-)
Here’s why I asked whether they belong to a church that celebrates Latin Mass: Parishioners at these churches tend to have traditional, pre-Vatican II beliefs. They might believe Catholics should only marry other Catholics in a wedding at a Catholic Church. However, the Catholic Church itself has no such requirements.