Query re pip phone assessment or paper assessment

Hi , I am needing advice regarding my 18 yr old sons pip phone assessment that is lined up for next Tuesday morning .

I am needing to support him ( as his advocate/ representative ) since he can’t represent himself effectively .

However I myself have communication differences and can’t process or answer questions put to me on the spot as in assessments .

He is awaiting an autism , pda & adhd assessments .

He has EDS3 & epilepsy diagnosed ( with u desirable effects from the epilepsy medication )

I’m familiar with the whole pip process , since I have a pip award myself & experience of 3 or 4 pip tribunals myself .

I have Asperger’s & in autumn 2021 when I had to reapply for pip , I noticed that pip didn’t even award me any points relating to autism which made me realise they didn’t understand Asperger’s at all , since these are well known areas of difficulty …

Please could anyone advise what I should do and say when I call the assessment ‘service ‘ tomorrow ?