Those children are innocent of your daughter’s choices. You’re not taking a moral stand by mistreating them and passing your anger towards your daughter in their direction, you’re just being cruel, cruel towards innocent children.
You and your family have been blessed with multiple children into your family. They’re in your family, regardless of your preference, by your daughter’s actions. If you chose, you could show them the warmth of God’s grace and compassion. You could shower them with love, affection, and spending time with them. You could bring them to Mass, you could bring them to charity endeavors, you could bring them to joyous and fun church activities. You could show them God’s plan for relationships and marriage and the moral compass, through actions with compassionate love. By abandoning them, treating them differently, directing your anger with your daughter towards them, or other things which are plain cruel… you’re not showing anything of that sort. By doing such, you simply harden their hearts towards you, your family, and potentially God and the church if they believe that’s the excuse you use for such cruel actions. They’re children, they don’t deserve that.