Who told you they need 2 areas of difficulty? I think you have been fobbed off
All LEAs have to assess for a statement, they will wriggle out of it f they can
My daughter is only physically disabled and has a statment, it gives her 1-1 support and access to physio/ot in school
As for the secondary school, he will just be counted as a 'normal' applicant without statment, so you will go through the same process as everyone else. You can try to get in on medical/social and should get letters from professionals to support you
If you get offered a place at the other school, you have a right to appeal. A panel of lay people will hear your case and the LEAs case and make a decision. Again, letters from gp, social worker (if you have one) paed, OT, physio (all or one) will help your case. You really need to be able to say why School A is the only school to meets his needs, so research all the schools and decide what to focus on. (you can't just prefer it iyswim) So focus on things like support units, size of school, facilities, access etc or anything your prefered school has that the others don't
I would fight to get him a statement though, as secondary is much much harder than primary and you may find he has more needs (ie tiredess, physio input/sessions,keeping up with writing, technology to make note taking quicker can be written into statement) A statement would help with strategies to help him meet his full potential in any setting and the LEA must pay as it is a legal document
It's really worth fighting for the school you want