Won't let me type the whole question above. If a Christian adopted a child who was a different religion, should the parent force the child to go to church? Should the parent prevent the child from going to temple/mosque/etc?
I love that we as Christians can expect God thru Jesus and the Holy Spirit, to meet us in the streets and homes of our lives. How being always and forever in us, we have His guidance and help to establish our steps. My answer is to pray. And pray and fast. To ask, seek and knock for God's practical will concerning this reality God has laid upon you.
Parenting is accepting our kids as they are, and never leaving them their to be uninfluenced toward love and good deeds.To invest in our children spiritually is, in essence, investing in their Eternal joy. It is the love God has called us all to propagate in our relationships with others. Be it a child, a friend, a brethren, or a non-christian, even our enemies.
Now, we look at Jesus and how He went about these relationships, He led first by example, then He led by planting seed of encouragement and warnings of Spiritual truths all packaged in genuine love, then we selected a few to invest in as those people heeded and not just needed Him. Then He was transparent, and even vulnerable by way of leading them into discussion and discovery of Himself and His values for them to adopt by their own will. He instructed what best to practice, and what not to practice, always sharing alongside them as to why, and for what purpose.
So going back to children of different cultures even though they are now apart of your current culture, we see a need as we discern this spiritually. A need to allow patiently a cross over from one culture to another, just as Christ allows His patience with us crossing over from death unto life in the way we live in Him now set apart from that old culture.
So, your story has a cross-roads. What we need to be patient with and what we need to invest in, in the way of proper alignment with God in righteous living. If these children are of the age to be under your care, then yes, take them to what God has made clear for you to invest them in. But parenting isn't about force, it's about doing, as we are apart of it with them experiencing it with them, including there hardships over it in understanding their needs to make a successful cross over. Ultimately they will be set to go by you which is ultimately forcing, but the goal is always to side step the concept of forcing into an agreement in going as you cultivate this in them thru questions and involvement of love in all areas of their lives.
This then will depend on their age, and understanding spiritually - etc etc...But the question here is how much trench work will it take you (or the parent) to love them toward having them seek God's face on all things? There's the prayer.