Would it be wrong to attend a wedding of two ex-Catholics, who are getting married in their new Evangelical church? Their church believes that Catholics are pagan worshippers. The groom is my nephew.
Since both the bride and groom have formally left the Church and are members of another church, they are not formally bound by Catholic marital law. Assuming that there are no obvious impediments to the marriage, such as a previous marriage or a close blood relationship, the Church would presume their marriage valid and sacramental. If you wish, you may certainly attend the wedding.