Does my red eared slider have metabolic bone disease?

Well your turtle is likely sick. Take it to a vet. Or give away to someone and tell them to take it for checkup cause it might be sick. If your parents are going to be this ignorant with your turtle's health and proper care and you can do nothing about it, you have no further point on keeping it, cause seriously, what can you do if your parents are gonna be so thoughtless? And no offense to you or to your parents by the way. And give it to someone who will really take of it, not to some of your little friends from 6th grade.