Is it ok for adult cats to eat kitten food?

It's ok for them to eat it. It's just higher and fat and protein to help the kittens gain weight and muscle and grow. The mom should be eating it as well as the kittens. If there's no way to separate them from the rest of the cats, just make sure they don't gain too much weight from it. Try to get them to exercise a bit more to make up for it.