I'm not sure how to answer about the baby, because I don't know if you were planning on taking him.
If you don't want him to go, I would reply "Yes, we are planning on going. I think it's best that you don't accompany us. If you still want your ticket, come pick it up by ____ o'clock. Let me know what you want to do because if you don't end up using your ticket I can probably find someone to take it."
That's what I'd do. This is a tough one because the plans were made so long ago and he's vague-texting where he's not being clear if he's just asking or if he expects to go.
Of course, this means that he might drive separately and be there, but you'll still be fine if he makes that choice. And you still get to lay down a boundary that it sounds like you want to lay down.
