Something someone said today reminded me of your post. They said "You can no more get someone sober, than you can learn to ride a bike for them. And if they don't want to do it, it ain't gonna happen."
I agree that it was a mean trick using the grand children to force you back. I'm suspecting that they want a live in Dad-sitter to try and keep him out of mischief.
What you do can only be your decision. But you only have one life. You have no responsibility for this man. He is responsible for himself, and only he can turn things around.
You deserve to be happy, joyous and free (as does everyone). I hope you do what you need to so that you can be those things. x