My mil worked for many years in the office at a Camphill school near Belfast. She loved it and said the children there were very happy. It still has a good reputation.

I think, as someone else has suggested, that shorter outings might be better until he and his carers or whatever name they give themselves, get to know each other. It must be quite frustrating for you thinking you're going to have a few hours to yourself only to discover you're not. Perhaps you don't even expect it now. I do hope a better arrangement for you and your son can be put in place.