How can I maintain a good diet?

I injured myself 10 months ago and I gained 20 lbs!!! I really want to lose it however it is hard especially since I am still injured ( my knee) so I can only do certain things. Basically I have these workout dvd's and I do yoga and walk. But when it comes to my diet I have trouble as it feels that my mom, dad and brother are being pigs by having donuts in the house or chips and it is really hard not to indulge. I just want to cry because I so want to get back my athletic muscular body but my family are pigs! How can I maintain a healthy diet that will help me with weight loss?