Hi there, I was in a mixed marriage with a Presbyterian for 23 years (he died). We were together 10 years before we got married. So 33 years in all. We were happy. His parents and most of his grandparents were Prebyterian, his only sibling married into a strong Baptist family (they are now nondenominational), and he had some Catholic uncles/ aunts/ cousins/ grands/ greatuncles and aunts. My own father was a convert and his parents and other family were Baptist/ Methodist.
My husband was a strong believer in Jesus as savior, but he wasn’t really into practicing a faith as in going to church regularly or doing any sort of praying. He just figured if he did his part to live a responsible and kind life then God would just take care of stuff without him having to bother too much about it. He would accompany me to Mass (stayed in the pew at Communion time and we did bicker a little because he wouldn’t genuflect as not believing in the Real Presence). Occasionally, like when there was a family death, I would get him to pray a Rosary with me or go to Adoration with me. He agreed when we got married to raise the kids Catholic. We ended up not having any kids for physical/ health reasons but I am quite certain he would have been fine with Catholic kids.
I tried to be respectful of his faith, but as I am a bit outspoken and blunt we would often end up with a “good grief that’s just silly” ending to our conversations. He didn’t mind too much. For my part I didn’t get bent out of shape when his father thought my making the Sign of the Cross meant that I was angry with my husband over something because he had been around Italians who would cross themselves at times when they were just about to fly into a rage. We had to explain to Father-in-law that that was just me praying.
The in-laws didn’t mind my being Catholic, really nobody did. I had an open invitation to go to Presbyterian church with them if I wanted to, but I didn’t want to, so I didn’t. I didn’t expect them (or even my husband) to go to Mass with me. It was all good. At some point his mom told me a story about her Catholic dad being upset when she left the church (her mother was Presbyterian, she picked mom’s church). I got the impression she didn’t get along with her dad over other things so that’s why she wasn’t inclined to his church. Later I found out I was apparently the only one in the family she told that story to.
I think if you are marrying into a family where they are all actually practicing their faith and going to church and really interested in religion, etc is really important to them it might be more difficult for you than it was for me, but really if you all just respect each other, don’t bicker a lot over religion and settle BEFORE you get married how the kids will be raised, I think it’s doable, especially if you both believe strongly in Jesus as savior. I was really hoping to get my husband to convert and praying over it a lot but like I said he died. The priest told me atterwards God may very well have granted my prayer at the moment of death. I hope so and I have good reason to think my husband is in heaven now so I just trust God about it.