You must have felt very strongly about your decision to get this far in the process. As you make better decisions about your diet and it shows in weight loss, your family will be facing their own dysfunctional eating habits and unhappiness with their weight/health status. You will be a constant reminder, so expect more resistance.
Don't sabbotage yourself by messing up your pre-op diet. As you know, eating is fun, but being fat and unhealthy is not. You know this.
Use this situation as an opportunity to take control of your life and honor yourself and your decision. Good luck and keep me posted.