Why can't he have the £250 in cash if that's what he wants.
I spent years training my Grandmother that her choice in clothes was dire and please give me the money.
Maybe, this seems a bit rude, but we weren't very well off and it was just a waste giving my DSIS and me things we simply weren't going to wear.
Likewise we would combine, birthday, Christmas, parental and family monies if we wanted something larger.
Gifts under the tree is very sweet, but gifts gathering dust is pointless.
Yes, it's the thought that counts, but thoughts go both ways.
Your DS needs to realise that he is a member of a large family and lucky it is financially secure.
You have to accept not many DCs have five siblings and very few 15y have two year-old siblings.
Compromise as always is the name of the game.