I'm sorry to hear about everything going on in your life Ringo, food is a crutch for most people here I think and it's totally understandable why you've had a hard time controlling yourself with so many stresses under foot.
I am in total agreement with Back2Barb on this one, you do need to see this through and stop putting your life on hold because of others around you. As for arrangements with your children, you're putting up your sister and her family, it's the least they can do is help out with them while you're away for a few days. Built in babysitters! Put them to work!! Haha
Stay strong and think about the future. All hard times give way and yield eventually to brighter tomorrows! Don't give up on this surgery or yourself. Make up for lost time and get ready to start this new chapter of your life!