At the request of DC, they're going to be responsible for eachother's stockings this year. I feel like this could be great fun or a nightmare 
DS2 (10) is buying for DS1 (17)
DS1 is buying for DD (12)
and DD is buying for DS2
£20 budget each (provided by us). All in agreement that it's a bit of fun and a nice way for them to start thinking about eachother a bit more. Wish us luck! 