I am so very sorry that you are having a difficult time and S10 is not there w/you as much as you would like. I agree w/Peacetoday in so many ways.
One of the things that I have noticed is that your w is a controller and wants to dictate everything including the time you spend w/S10. She knows that you want to spend time w/him very much...so, what does she do, she uses him to get back at you, to hurt you. I know that this is going to be extremely difficult for you, but you've got to let go of him for a while. I do think that if you don't show her how much you want him there w/you, she may eventually allow it.
MLCers are like children. Children want what others have and when they get it, they do not want to share and will go to extremes to tease/tempt others and then take away the toy. I think she's using your S10 to attempt to control you into doing what she wants.
For now, you have to have faith, faith in the man upstairs for he is the only one that can get through to her. Have faith that your w will do what is best for your son and that some day soon, he'll be reunited w/you and his brother. Try to focus on you and your S9. Find a way to help him because he is suffering too and needs to know that both of you love him as well as his brother.
Drop the rope a bit, try not to appear to anxious about your S10 around her. When she senses that she's lost that control, she very well may lose interest in sticking it to you.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.