I am glad he is bonding with yourself and your grandson. Get to the library and you can pick up any basic dog training book, and you and your grandson can both work with him and help teach him things. Even learning simple commands like "sit" and " down" will help him, as he will be praised and rewarded. Walks on a leash, even short ones, will also help build his confidence with the world around him. Love, patience, and learning will all help him recover from his past and become the great dog he was always meant to be.