My initial response was going to be the "Sorry, that won’t work for us." But Liz really brings up a good point. In this case, I would extend to "Sorry, that won’t work for us. We're celebrating just DH, DS, and I this year." I feel like saying "immediate family" she will take liberties with. No wiggle room for her to push her way in. Practice practice practice. No explanations. No additional info. Just rinse, repeat. Good luck!