Yes, they are usable. Fluff up the soil that was under the stepping stones, throw down an even layer of the grass seed (not too much). Keep it watered. You will see sprouts in about 1 week depending on temperature. I don't recommend using fertilizer at this stage.

Thanks B, that's great news. It's perhaps a bit too cold here yet but that's what I'll be doing.

The birds are getting excited already Hank...