((OneLessLonely)) - it's tricky when families start falling out and fighting at the best of times, let alone at a time like this. But I know you can get through it without drinking. Whatever happens, remember that your sobriety has to come first, and if that means finding an excuse to rearrange/cancel the meal, then that's what it means.
Love and Hugs to you, and remember that whatever happens, nobody is going to die as a result.