That sounds very positive and a really good idea.
They use horses quite a bit for therapy these days, so I would imagine it is quite helpful for your other son.
Good luck and hope you find something so your son can build skills and self esteem. Slow roads but that's the nature of these things. Lots of people do lots of things outside of a school education. No road has to be a straight one 😊
Take care and all the best,
Linda