The whole family is so used to Dee's control freak behavior that we sort of tune out. Phil and Lupe will generally say something like "Dee, he's fine right there." Lupe and Phil are good to be with-- it's just Dee's antics that s---w the dynamic up.
So they do say something? - that's good. As long as you aren't jumping to follow orders every time Aunt Dee gives them (and she's not banishing you from adult company), I think you should just let her words roll off your back. Just ignore her. If she says "go get Christopher's toy" dont go get it. Say 'He doesnt need his toy right now' if she persists 'I am enjoying lupe and phil's company, and christopher is fine. if you think he needs his toy, I wont stop you from getting it for him'
She sounds like the type of person that needs one good person to stand up to her and then she will hem and haw, but she will stop ordering you around. good luck!