My mom is and my dad has adopted her religion though he was born and raised a Catholic.
Basic History...
Mom was born & raised in a Reform household.
Dad was born & raised a strict Catholic.
Married in a Synagogue , dad converted but just for the technicality. Children were raised to respect all religions, celebrated Hanukkah with one grandma and then went and celebrated Christmas with the other. Dad never gave up his faith in Jesus but he hid it for many years. His faith moved away from Catholicism and towards a more 'progressive' version of Christianity that he basically made up to fit his current situation.
Mom started listening to Christian friends, reading the bible, etc... looking for more understanding in our 'mixed' household. She eventually became a believer in Jesus Christ and started looking for a church. She (and the rest of the family) never really felt comfortable in any of the churches that we tried and religion just became a personal, private thing again.
Mom met a messianic Jew and it was like the figurative lightbulb above her head. She started attending service regularly and dad starting going with her. They, as a couple found a religion that was right for both of them. It respected the Jewish faith that mom was raised in and allowed her to worship Jesus (Yeshua) without feeling like she was betraying her family and her heritage. Dad just found it to be a good compromise : )
I'm the oldest of 3 boys and I'm an agnostic. One brother is now a Lutheran and his twin is a practicing reform Jew.
Religion can be confusing : )