We are making strides in improving representation in many areas of diversity, but disability rep is still light years behind. It feels like every day a new book is published with poor rep. Disability rep needs the same care as other areas of diversity. Some suggestions:
Use ALL of your resources. @DisabilityInLit is fantastic. Take a few hours + reading through that website. Sensitivity readers are ESSENTIAL to disability rep. Don't just have your nephew read it. Use sensitivity readers that represent throughout the spectrum of the disability.