@Reece Sorry to hear that. So it only does that outdoors? Did you tame a feral cat?
Gentle biting is just showing some love, though occasinally the claws may get deep just because the cat feels well. But if it's all claws and biting.. if the cat is older it is probably not possible to change this behaviour. Then i would just advise to let the cat be when it's outside, and tell the grandchildren not to play or tease it, when being outside.