Yes, portion control. You can have what they eat but watch your portions. If they have a veggies, fill up the plate with those first. Take a palm size of meat. Pasta and starches keep to a minimum. Go shopping with your sister in law and grab some salad bags so you can have some at dinner. Offer to fix a meal for them. Pick up fruit and snack on that. Walk as much as possible. If you can come home the same weight you go, your doing great.