Would it help if the next time they ask to speak to S10 you just encourage them to give him a call? As siblings, they should be able to speak to him whenever they want. You may have to follow an agreement re times, etc. But the kids should not.
You have to remember that you cannot force people to parent. If she plays games (sending them to others) so the kids aren't together anyway when they go over there, why not just not bring it. She probably won't want to see the others given her mindset.
I'm so sorry you are having to deal with this. I know how badly I suffered the loss for my children when their dad decided not to be a parent. But you know what, they accepted it long before I did and my inability to accept it just brought them more grief.
Nothing has to be permanent or forever. Sometimes taking things one day at a time is hard enough.
