Ellie -- Your sisters may not exercise now but eventually they should. If they are skinny and not exercising they may have a higher percentage of body fat than you, and they are considered a skinny fat person. You on the other hand if you follow the BFL style of eating and working out will in no time, be in fantastic shape...
Hey welcome and congrats!! that is so amazing! thank you for the inspiration! I really think you'll love it here these people are awsome!! I am new to this site as well. And at losing weight and I feel I can do it now that I have found this place and these amazing people!!