Primary School Application - Exceptional Medical/Social Needs

Hello everyone

My son is due to start reception in September 2018.  He was diagnosed as an ASD child in January 2017 and currently is being assessed for an ECHP (literally just received the letter to say that the LA had agreed to do the assessment).

However, I have not yet sent off the online form for a reception place which is due in 5 days time - on the form there is a section called "Exceptional Medical or Social Reasons" - do I need to click yes to the medical reason for his ASD diagnosis? or is this part of the form for something else?.  The school is a mainstream school with no unit attached.

Also, his sister goes to the same school and the school has a sibling priority - would it be better for my son to be admitted in the school under this instead?

Hope this makes sense!