I think you have it figured out pretty well. Eventually, it is a battle that has to be fought, but this year might not be the time. In the end, I think he needs to stand up for you, and stand up to his mom. But he might not be able to do that yet. I think it would be a step forward if he was able to just tell you that he doesn't agree with what she is doing, but doesn't feel that he can fight it right now. It's not ideal, but it's a step in the right direction.
