I think by not eating it, they'll get the picture at how serious you are about weightloss. DH would say...lets go have pizza and I'd give in and go. Then when I got really serious about dieting and he would ask, I would simply say "I can't eat it" and he learned how serious I had become.

(((HUGS))) I hope that your family gets onboard. Its so much harder when you don't have their support....tell them that!