I simply don't understand all this extended gift giving! Let me try to explain; n my opinion, buying for adults goes something like this........hyperthetically, I goe to the shops and spend £30 on a gift for each my adult family members, each one of them does the same, on Christmas Day we potentially end up with loads of stuff we either don't want, like,or would ever use! Who benefits?..........the traders!
OP, instead of feeling obliged to buy for the in laws why don't you offer to supply some really good wine for the day or an extra special box of chocolates to share round?
Gifts for children are different in my mind but the endless buying for adults when you know you'll feel aggrieved afterwards plus all the stress and expense just doesn't make sense to me.
Instead of a personal gift for DS and DIL I would be tempted to give them a joint gift too, you might get more acknowledgement from DIL that way.