Nonnie,
I am sorry for all the pain your son continues to cause you and your family. Addicts are the best at lying and creating drama. I know it hurts not seeing your Grandchildren, but it sounds like she is holding you hostage. She is punishing you for protecting yourself.
You need to do what you need to do. Your daughter will get "screwed" by her brother soon enough and then hopefully she will be open to communicate again. I am sorry that you will be "losing" both children, but for you own sanity I would do what ever you can to protect yourself. Hugs, we get it on this forum.