Children at different primary schools, eldest has ASD

Hi. I'm looking for advice really. As the title says we currently have two young children in different primary schools (not through choice) and the eldest has ASD (not yet formally diagnosed despite trying to get an assessment for over a year now - another long story). We think that moving him to his younger sister's school would be catastrophic and he wouldn't cope and there is no option for my younger child to move to the other school because it has a long waiting list. We've been told we don't qualify under the "exceptional medical and social needs" category because he isn't deemed bad enough, only being on the SEN register and not having an EHCP. We've done two schools for a year and it's put us all at breaking point and my husband is now severely depressed as a result. My son screamed for an hour today after I had to get someone else to pick him up because I was at the other school (I usually pick him up and ask a friend to get my other child). He's also getting anxious in the afternoon at school and being sent to sit in the office. People seem to feel that his needs are minor because they're not obvious but as I say it's left us at breaking point and we are not sure how to cope with another three years of this. Therefore I'd be very grateful for any advice!