How do i stop a family of not training their dog well?

a friend of my cousin has a german Shepherd and they do NOT train it how a normal person would. the play very aggressively with that dog (i.e. when the dog is chewing on a bone or something, they will start to play "tug of war" with it. then it starts to growl.) also they HIT it, just for fun. not abuse, like slapping it on the face or something. my uncle told me how the dad would say, "hey! watch this!" than he would hit it. they are always saying that it will never hurt their children and it will always protect them. but, my aunt it afraid to be anywhere near that dog without one of the owners with her. and if you are just sitting at the table, the dog will come up to you and put your arm IN ITS MOUTH! when it does it to my aunt, she said how she just froze and couldn't move, because once that dog thinks she is going to hurt the kids, there goes her arm. and this german Shepherd is 115lbs and still not fully grown! a normal size for a full grown male is 85lbs. whenever they invite my aunt over for dinner or to watch a football game or something, my aunt always says, "no! come here instead" because she is terrified of her kids' safety around that dog. when the daughter is playing TAG with the dog and in a "playing matter" the dog will jump on her. almost like tackling her. but it is just playing. my aunt was talking to the owner and saying how what if your son has a friend over and they are playing wrestle, than it looks like the friend is attacking your son, so the dog will want to protect him, and next thing you know, you are in the hospital about to get seued by his friends family. i dont know what to do, i know its not the dogs fault, its the owners..... HELP!!!!!!!!!!!!!!!!