So a couple of problems. He’s adorable by the way. With your sister, it sound like he is different with her because he does not regard her as the pack leader – possibly as a rival – and he needs to learn his position in relation to everyone in the family not just you. I dont have much advice, except to read about the Nothing IN Life Is Free (NILIF) program below – let me know how you get on!

As Daphne says its probably a thing with your puppy thinking he is top dog or at least higher up than your sister. Daphnes suggestion is good. There are various ways of training your dog (my ex used clicker training which worked well) If he is particularly agressive with your sister then you really need to get her to do some of the alpha male roles too (feeding him after pretending to eat some of the food herself, having hold of his favourite toyand not letting him have it until he obeys her. IF it is a specific thing like biting she should try completely ignoring him when he is behaving badly then once he has stopped and is sitting down start to play/praise/treat him. As to chewing its a case of keeping a close eye on him and catching him in the act then gently reprimanding him for it, if your not there when he does it there is no point in telling him off afterwards