At the moment, I've gone with the notion that the Holmes brothers use a complicated bartering system of favours as presents, which goes along with your second idea.

The problem is what Mummy might get for her boys, and what she might get for them. She can be sentimental, of course, but it wouldn't be appreciated. I can sort of skim over most of it, but I'd like to mention a few specific things they received. I think I have what I need now. I just need something Mycroft might give her. I didn't think she'd be hard to shop for, but she is! LOL

Stupid fictional characters.