Help with form filling for an assistance dog

Hi all who read this. My wife and I are about to start the process of form filling to qualify for an assistance dog through a charity. We are at the early stage of the process and have a lenghty form to go through.

Has anyone had any experience with these type of forms and how to word things correctly so the relevant information can be given and what errors to avoid. Our son is14 and as well as having  higj anxiety autism ( with ticks)he also has PDA and ADHD. 

Any help would be greatly appreciated 

Mark and Angie