Losing your family for joining the 'Mormon' church is pretty common within the religon. As for the age gap, if she were the younger one, nobody would even blink an eye (with him being 26 and her 20)
If the situation were reversed and it was my 18-year-old daughter being sucked into religion by a 25-year-old mormon dude I'd be pissed. Especially if my daughter was an up and coming musician and the dude was a gold-digger. And forget the religion or the gold-digging, the age difference alone would raise red flags.