I’m the product of such a marriage.
My father is Jewish, and my mother Roman Catholic.
My parents talked about it before they married, and in their cases it was a relatively easy decision: My father is non-practicing and agnostic, while my mother practices. Both felt it was important that my sister and I be raised in some church, and with my mother being the one to practice - it was her religion that we were raised in.
My mother’s parents had no problems with the arrangement AFAIK. They accepted my father as their son-in-law, perhaps even as a son. I know my father ended up being closer to them than he’d ever been to his own father, and I closer than he was to his mother, too.
My father’s mother was a different story. First, a word of background. You may not have met my grandmother in life, but you know her. She’s the Jewish grandmother of all the stories and jokes. Genuinely wanting the best for her family, but also very firm in what the best would be. And willing to use any kind of emotional judo to accomplish that.
To say that there were fireworks when my father announced his choice would be an understatement. Obviously, I wasn’t around, but judging by the winces, and the one comment my mother will allow herself to make, it was a donnybrook. My mother’s comment is simply: “Thank God for the Rabbi.” AIUI, my grandmother’s Rabbi, not just her preacher, but a lifelong friend and mentor, too, basically pointed out that my grandmother could either accept my father’s decision, or she could come back, hat in hand, when the grandchildren were born.
Even with that, when I was 20, my sister 16, and my parents had been married 21 years, my grandmother said to my father in front of my mother, with my sister and I in the next room in her little apartment, “Rosemary is such a nice girl, but are you sure you couldn’t have found a nice Jewish girl?” :eek:
So - my experience is that it can work, but it does open up more than a few cans of worms.
On preview, I don’t know how it would work with two people who are both committed to their respective religions. Very understanding would be part of it, yes, but…
And, of course, for marriage in the Catholic Church, with one of the members of the marriage not of the faith, still requires, AIUI, that the non-Catholic agree to have any children raised Catholic. Which can’t make things any easier.