In chapter 222, we learned Shigaraki's backstory. It was pretty much what I expected.
The doctor says "this is what remains of you're family" when he introduces the hands which makes me scratch my head.
We saw in this very chapter when Shigarki's quirk disintigrates something (we saw him do it to a dog) it disintigrates them completely, not the entire body except the hands. The hands are all of uniform size and what's more, even in the brief flashback they still have a box at the base of them with holes drilled into the bottom.
I'm going to guess that these hands are manufacted objects which ashes of his family rather than literally being the hands of his dead family members. It's also entirely possible that All for One killed Shigaraki's family himself then wiped Shigaraki's memories beofre transferring to him the decay quirk (I don't like that theory however).
I immediately noticed a parallel between Shigaraki's backstory and Eri.
Shigaraki's ethos as a villain remains somewhat vague. Until now he'd been pretending to follow Stain's ideals but in this chapter he revealed his true desires. Interestingly, Dabi seems like he's still onboard even after hearing this. I'm not sure how much longer Spinner will be oboard though.