Just be honest with them, and without judgment, when they want to talk about issues. Let them lead the discussion and make it appropriate for each age group. You can tell them what you believe, without impugning her. As parents it is our job to talk to our kids about relationships, morality, and ethics. I don't believe a schism in the family changes that obligation.
My children know my stance on marriage, fidelity, and trust in relationships. He does not talk to them about these kinds of issues and they do not open their hearts to him. You will likely experience the same thing. Kids have good antennae. They know about problems in the relationship long before we tell them. They know who has their back.
Try not to borrow trouble and take each day as it comes. I have worked a lot with my counselor on not catastrophizing everything and just standing back and dealing with issues when they actually arrive. My anxiety is way down.
