Do you spend four times as much on your DN, than your Dsis spends on your DC?
If not, is it fair that your DSis has to spend out, say £80 on your DC when you are spending £20 her DC?
I have more DC than my siblings, and feel a bit guilty that they have to buy more nephew/nieces presents than I do. If DB buys my DC a £10 gift each, should I therefore buy his DD a £10 gift or £30 gift? 
But, then as I have more DC and earn less, I have a smaller disposible income....
I'm over thinking this, aren't I. 