My brother is getting overwieght, what do i do?

ok im 17 and my brother is 14. i am normal wieght athletic, and my brother is kinda overweight. honestly, i think it is sad because he is my brother and i feel sorry for him. my parents got divorced two yrs ago and i think thats why hes fat, cuz hes depressed. but my mom (who i dont see much) denies that he is overwieght. my dad knows but he still cooks us high fat foods. i tell him to make us low fat healthy foods, but he doesnt. i really do not know what to do about my bro because everyone doesnt even realize it. just me, i look at him and im just like ugh, what should i do???? PLEASE HELP ME! (and btw dont answer to diss my bro, cuz ill eff u up, he has lots of friends and popular smart kid, and good at band) BUT PLEASE GIVE ME ADVICE! THANKS