Sorry that you are going through these hard times. Does your sister know that you are a recovering alcoholic? If not the BBQ may not be the best for you based on what you have written.
Maybe you can drop in & stay a while & make your way back home before things start to get out of hand (people getting drunk). Can you show up an hour or two early & help her to prepare & spend some quality time together (maybe let her in in your decision to quit) then when you are an hour into the BBQ roll out on your merry way.
Maybe take a day to yourself & let her know why (or come up with one of a million other excuses). I dont condone lying but when your sobriety is on the line let the white lies fly!
Take care & please dont pick up that first drink... you know where it goes from there.
NB
