Older dd1 already at secondary school, often doesn't see some of her friends from one day to the next.
The year is split into two, for logistical purposes I assume, and whilst one half of the year is doing one timetable, the other is doing on the opposing timetable iyswim and the twain don't seem to meet.
It's a big-ish school, although probably small in comparison to some. In our case, before dd went they were interested to know if there were particular people she wanted to be around (or not) and seemed to take on board what we said when allocating tutor groups and timetables.
If you feel ds and dd would benefit from a bit of distance where possible, I'm sure the school would be interested in your thoughts. I should hope they would be interested in speaking to you anyway in order to help with any additional support your ds may require to help him settle in.
I do think two separate schools - or three if you have another child at a third school too - would be tricky. Also, although I have no experience of Autism, (many other posters on here will be able to advise more than me), I'm guessing your ds would find it v reassuring to know his sister was there at a new school too?
My older dd is very
at the mere thought of her younger twin brother and sister joining her school the year after next. She says she's going to ignore them. Nothing like a bit of family solidarity is there?
I know though that although they annoy/embarrass each other they don't mind nearly much as they make out and will support each other. Teenage girls will always find something to angst about be it their brother or their hair or each other.
What I'm getting at is that your dd may possibly be reacting not so much to her brother's autistic traits, more that she is getting to an age where he's just her brother and therefore embarrassing, full stop.
That's certainly the case in our house and tbh my ds does know how to press all the right buttons. He's 10. That's what many 10 yr old boys are like with their sisters and their sister's friends
. I may be wrong. As I say I'm not experienced with autism, but I am with 10 yr old b/g twins and how they can annoy each other and how at the same time they are close. Much of what you say sounds familiar.
I am quite sure if any of mine thought there was any mileage in it they too would make a pretty good case for each having a different school.