Welcome to SR.
I can't really add much that hasn't already been said. In my situation, I try to worry more about my emotions, reactions, thoughts, feelings. My AW is a grown adult and can deal with her own problems.
Once I'm clear on my stuff, then I can make sure my son is taken care of. Bad as it may sound, you absolutely need to put yourself first because if you're not well, foggy, unclear, scared, etc., you can't do anything for your son.
Enjoy those cookies with the boy and grandma in peace. You deserve it and so do they.