Is there a place my sister and her son with MS could move to where he would have the care he needs?

Newark Ohio has several group homes. Plus, he will need to sign up for Medicaid and get a caseworker assigned to him. Call the Center for Disability Services. Address: 175 S Williams St, Newark, OH 43055
Phone:(740) 344-2995

Where do we find such a facility. That's our problem.

What he needs is a group home, with fellow residents his own age and staff on site 24/7. Do what is good for him first and foremost.

I think you sister and nephew need to plan for the long term and face the reality that she won't be available to look after him for much longer, at least not in a hands on way. It sounds as though he really needs skilled nursing care or at a minimum assisted living, if she is functioning well she could consider an independent living apartment which is near or attached to his new abode. I know they won't want to take that step, but better to plan now then to wait until her health fails and the changes are pushed through in the midst of a crisis.