A little long, so a minute or two longer than I normally intend another to read a response I give (skip to #6 if it is more convenient):
Bryan is a better person than me.
They want four children.
I must find more real positives about the Roman Catholic Church. (This is a hard exercise for me but everyone needs a second chance sometime.)
My kids have not found mates being young yet.
1) I pray they find Godly mates.
2) I will have to live with the degree they understand the gospel of grace, being unequally (or perhaps equally) yoked.
3) I will continue praying for them and my grandkids, to love the Lord God
4) I don't know what I'd 'do' when/if it came to one marrying a Catholic.
It carries a large chasm and that alone carries grave consequences to the seriousness of what grandkids will hear concerning the Scriptures and importantly the gospel of Grace. Both the Catholic AND the Protestant compromised or weren't grounded or neither could have married the other.
5) Grace God may yet use the union to bring His purposes. I worry for a couple that have lost their life-driving purpose, both the Catholic, and the Protestant. Compromise means both of them have other things on their minds and other goals. Especially your grandkids will need to hear grace, and so I'd pray for opportunities to grace your grandkids as well as grace your daughter and husband. In my family, it is ever my prayer to grace the unbelieving, and bring them to the throne of God, and grace of Jesus Christ. I also pray often for the Love that covers a multitude of sins and doing it wrong, that Christ will shine beyond both my obvious rejection/disappointments and that He may be seen. I very much resist going to a Catholic church for baptisms, funerals and some marriages, but that's the stance I have chosen. I think it important, again, to fight the battles against the gospel that you believe God has called you to personally fight, and to allow Him to fight other ones while loving and gracing them. We worship God in spirit AND truth, thus you will tend to choose based on that spirit/love/truth tension. I don't think, if you are ever conscious of uncompromising God's truth, loving as deeply as you can, and walking not in your own strength, but His, that you can make a mistake. My prayers are with you.
6) I pray for me, and my continual contacts. I have to be about Christ's business and I stand up against lies and mistruth but I try to ensure that I fight the battles Christ brings me and not pick others, to pray often for myself to be whom I need to be, and that they will encounter Christ more often in their daily lives. I try to remember Christ is Sovereign, and to do only the part I've been called to play while allowing Him to be Sovereign. Paul said he planted, another watered but only God gave increase. I don't always know my gifts, but I've tried to learn to do that which I've been called to do.
I had to learn to trust Christ for my step-father. He was Seventh day Adventist. In my youth, I tried sharing Christ often with him until the day he told me "don't ever share this with me again." My 'part' in the gospel was diminished to prayer, and being a light. Almost 30 years later, my father made a profession of faith and was a changed man. Someone else was part of that, I had to be satisfied and content that my part was limited and to know more specifically what part I was supposed to play and to realize it wasn't the part I had thought. I prayed often, and prayed too my life was a light and reflection. I am humbled and praise God often that He cared for my step-father and brought him to salvation.
I pray some small service and or meaningful conveyance finds you in these words and my story. I do not know my part in your life that will be played, but it too is a very very small part, and so I've prayed and will pray more for you and your family. His presence, comfort, and blessings -Lonnie