Simply put it, if you can't tolerate or understand each other's religious/spiritual views, forget it. You'll only regret this in the long run. The simplest solution if neither of you wants to convert is to either tolerate and understand each other's religious obligations, spiritual views and help each other with fulfilling them, or just go separate ways. If you chose the former way, remember that the problem will crop up again when you have children.

My fiance and I are both Buddhists, but even we have glitches. Why? I'm a more to Tibetan Buddhist but he's brought up in strict Theravada Buddhism (Like in Myanmar). His mother doesn't like me because I'm not "spiritual" enough in her eyes, but his father is thankfully more liberal. We made it clear from the start of our relationship though that neither of us is going to change this fact and have accepted it, even working together on this issue. As for kids, if we have any they be exposed to a healthy mix of both and they will choose themselves which path they want. And as for his mother? We chose to ignore, after all, even if I DO become "spiritual", it will still never be enough to her so no point trying to please her. After all, this is our lives, not hers.