Does your dog know "leave it" and "down"? If not, train him now. If he is herding your family (nipping at legs), use a normal tone of voice and tell him "down". Reward with treat, petting, and praise, gradually omitting the treat. If you have children that he is running down, he needs to learn that the correct response to moving children is to lie down. This behavior can also be curtailed by putting a toy in his mouth and making a game out of his finding a toy and carrying it around.
If he is mouthing you to get your attention, tell him to leave it, rewarding when he takes his mouth off you. It would help if you gave him another cue to let his wishes be known. For instance, if he sat at the door if he needs to go out.