My sister wants me to get fat! ...or is it just my imagination.?

It's not your sisters who should keep in mind that you're dieting - it's you who should have and keep self-control. It's your decision - yes, having a helpful family is great but it's all up to you. Not them. So if you want to lose weight, concentrate on what motivates you. Ignore your sisters - if they offer you something you shouldn't eat, simply shake your head (even if with clenched teeth, say no). The hardest part of a craving is the first 15 minutes. That you can take if you try to distract your mind. Good luck.