What could a male teenager do about his weight?

I hate being fat. I am a fourteen year old guy, 5-11, and 238lbs. I dont have access to a gym, gym equipment, I don't even have anything to use to substitute or improvise. My 18-year-old brother is so discriminative about me being obese, so I don't feel like doing anything. Everyone in my family seems to be fit no matter what they eat, so our entire apartment is filled with NOTHING but junk food, and my mom never lets me choose what to have at the grocery store. She refuses to get me into a gym or YMCA, not that there's one near us, anyway. It's tough having no father, because my mom never taught me how to be tough. I also have a little 5-year-old brother I have to watch over, so sometimes I can't even exercise if I wanted to. My mom doesn't have any money, so its a miracle if she is able to afford oil, never mind weights or dumbells for me. Are there any alternatives to my situation? My older brother wont do anything about it. I want to not only lose the fat (everywhere) but also gain muscle.