My family won't listen to me and they're harming my dog?

My mom and step dad think they know everything about dog nutrition because they had dogs like 30 years ago (And obviously we know way more about dog feedings and stuff now) but they insist on feeding her table scraps and bones like crazy (If we ever have any type of meat they give all the leftovers even if it's like 2 whole pounds of steak and bones, I'm not exagerrating at all). Well anyway, heres' the problem; they feed her so much that she refuses to eat any kind or amount of dog food (she's holding out for more human food) and she is so skinny you can see her ribs (And she's a husky!!!) and when I try to tell my parents that they're doing wayyyy more harm than good to the dog and that dogs don't need variety like humans, they just say they know what they're doing because they had dogs 30 years ago-_- And they seem to get mad when I tell them to stop feeding her human food so in spite of me saying something,they feed her human food. Help please! How can I convince them to stop?!