Applying for ILR for a 19 year old with autism

[rubatroid]

Hi there,
I have tried to find the answer to my question elsewhere on the site but found nothing which quite answers it.
My friend (who doesn't speak good English and so i am helping her) has a 19 year old son with severe autism. She has already completed 6 years of discretionary leave and is now applying for ILR using the SET(O) form.
Her son is completely dependent on her, cannot complete the form himself and cannot sign his name.
However, the guidance says that only children under the age of 18 can apply on the same form.
My question is, should she:
a) include him on the same form anyway, and explain why in the covering letter, including medical proof that he is unable to complete/sign the form himself?
b) complete a separate form but don't have it signed, explain why in the covering letter and include medical proof that eh is unable to sign the form himself?

Thanks so much in advance!
Reuben

[vinny]

Probably b).