Contact the NAS for advice. Their NI contact details are
here.
The phone number is 0845 070 4002, then press option 5.
Your brother is attending a special school and has a statement of special educational needs. There must be something on his statement about coping with behavioural problems. The school cannot be allowed to throw him out like this. They need to support him, and understand the difficulties he is facing in dealing with staff changes.
You may like to have a look at Glencraig, but I personally wouldn't want any relative of mine going there. I don't know if children
can even go as day pupils. But I disagree with much of their philosophy. I do not think they help people to achieve to the best of their potential. They are anti-technology. They run a farm and are staffed mostly by young people from mainland Europe on their gap year. I wrote some of my impressions on Camphill on
my blog here. The comments from Camphill ex-staff are very informative. One person agreed with an observation that the schools are 'like sugar coated prisons'.
Do not agree to let him go to Muckamore. That is serving as a prison now, with no sugar coating about it.
A further option to consider, is home-education, also known as home-schooling. This is how my autistic son learns and it means that all the stress of dealing with inflexible education authorities is avoided. It is a perfectly legal option, and although it may sound as though it would be so much work, it is worth considering how much effort goes in to getting a child ready for school every morning, dealing with problems at school, calming a stressed child after a hard day. You and your sister need to think about what is best for your brother and yourselves.
Good luck.