You should co-operate with them, they are trying to be helpful, not nosey, you see they have about 12 bulkhead seats just behind business class, where you have much more room and bigger seats/space than economy [ you also get business class food] and anyone with medical problems gets allocated those seats and then the business class trained staff can keep an eye on them during the flight.,they wont be there alone, at least 1 family member will be allocated too and if there arent any other "special needs" people travelling that day you might get lucky and the whole family get allocated.
Make friends with the special needs team when you phone , they are your link,and always phone them a few days before departure to confirm everything.Virgin are extremely helpful, pls dont be suspicious and accept their help.
I travel to Las Vegas on Virgin with a Downs syndrome lady an so far [4 trips] they have allocated our party of 3 to stay together in bulkhead seats, my husband is blind and we also get similar seating when we travel, they just have to be certain that you are a genuine case and not "putting it on" to take advantage of their care. truly I cant fault them.
Another airline might just let you get on with it !.
happy holiday.