Hi Waxwing
Your brother needs to concentrate on the difficulties that he has with walking. Is he slower than someone without his difficulties - are there any safety and reliability issues? - (which clearly there are).
Have a look at the advice in the guide about reliability and safety. (This is on page 16 of the old guide) and then more on page 75. Make it clear as you have done here about his need for assistance.
BIS
Nothing on this board constitutes legal advice - always consult a professional about specific problems