If it wasn't for the bachelor/ette party and shower I might have given them a pass.
We don't know the background, it's possible that they had, for whatever legal reason, to get 'legally' married years ago, but they sure didn't want to showcase it (not inviting people), maybe the two parties where sprung on them by their family and that's not what they wanted in term of celebrating.
Maybe they've finally saved enough now to have their BWW and also want to be 'church' married...
Anyway, as an invitation is not a summon, a gift isn't compulsory either.
You can put the accent on the religious part if you share their faith, just send a card or some sort of acknowledgment.