Only Mormons who are living the higher commandments of The Church of Jesus Christ of Latter-day Saints can enter into an eternal marriage in a Mormon temple. However, if a Catholic and Mormon want to marry, they can do so for the duration of mortality wherever else they choose. A good example is the family of basketball great Jimmer Fredette (https://www.mormonwiki.com/Jimmer_Fredette) whose father is Mormon and whose mother is Catholic. Jimmer’s parents gave their children their choice as to which church to join.