Agnostic and Devout Christian

Hey everyone! I'm a 31yo guy looking to propose to my 33yo girlfriend. We've been dating for about 2 years. We have been living together for 4 months and everything is going great. Our only indifference is our religious beliefs. I was raised as a catholic, but am currently agnostic. My girlfriend is a devout Christian.

I've recently asked her dad for his blessing to marry her, but was told that he needs to talk to his daughter first. Immediately after I talked to him, he talked to his daughter and said that he needed to talk to both of us about our future. My girlfriend said she wanted to talk to him on her own, but she has yet to do so. She is now reflecting on her future with me, and is really worried what impact our religious beliefs will have, especially when it comes to raising children. She is also concerned what her family and friends would think of our relationship. By the way, she hasn't told her family/friends that we live together.

We share the same morals and values and love each other deeply, but we both keep asking ourselves if this will be enough to have a successful marriage.