Wow, what shocking news for your family! I'm sorry its been such a battle for them to get help and answers.
I don't know anything about auditory neuropathy sorry, but my father is profoundly deaf and has been for most of my life.
He now works as a social worker/advocate for deaf people, particularly children, in Wales.
He is a big fan of the Deaf Association here in NZ, they offer great practical support, advice and community for deaf people and their families. They also have social groups, events and clubs for deaf and hearing impaired kids. They'd be a great place for your sister to contact.
Hearing aids are awesome now and practically invisible so if he needs them they won't be obvious to the other kids.
Have they discussed whether a cochlear implant would help your nephew?
My father had one of these put in 2 years ago after 50 years of progressive hearing loss and he can hear almost everything we say now. I hope this is an option for your nephew
I hope at least some of this is helpful to you! Big