The spines are just a part of a removable outer layer that splits open when the nuts are ripe. They're totally edible. (And the nut itself looks like what Akebono is holding - hers just has an insect eating it.)
There are lots of chestnut trees where I live and the spiny fruits are falling with the leaves at this time of the year, but I think they are too small to be edible. When you step on the kernels, there seems to be nothing there to be eaten. The only ones who manage to eat their shares are the crows who are always around the trees waiting for people and cars to crush the chestnut fruits.
I think what Knite meant is Yukikaze ate the chestnuts without removing the outer layer. I'm not sure if beavers or hamsters can eat such spiky things, though.
This is a minefield!October 19th
Went to gather the chestnuts in the nearby forest this year too. If we fill our baskets and give them to Mamiya-san, she'll make us lots of delicious chestnut rice.