How would you discipline this child?

hi there i need some advice on how to deal with my 3 year old nephew who to a bit to say the least. i have 2 children and my sister just has my one nephew.not to sound awful but from birth my nephew has been hard work for my sister and he hasnt really gotton any better as he has gotten older. he is very violent,aggressive and is always seeking attention.basically if he wants something my sister or my sisters partner gives it to him.the problem i have got is when i take my daughter who is 3(same age as my nephew) to their house he is constantly smacking biting and pushing her.this has been going on since they were 1 year old and my daughter gets sick of it.now i no kids fight but this is every time we go up there.and my partner is getting sick of her coming home with bite marks etc. like i said he gets his own way all the time.now for instance the other day me and my daughter were at their house as i was babysitting as my sister was at work.he was ok when i was there but when his dad walked through the door he started crying and screaming (which he does a lot). his dad had not bought him a chocolate egg so my nephew started kicking screaming.the next thing he picked up his play golf stick and hit his dad round the face.his dad told him off slightly and then went to the shop and got him chocolate. i couldnt believe he had given him that after what he had done.oh and then he hit me in the face with the stick.i just cant understand this child.i no he is my nephew but swhen me my sister my daughter aand him go out its kind of embarrasing.ivre tought my daughter boundaries i thin k and he doesnt have any.i have tried speaking to my sister about his behaviour but she got in a mood and refused to talk about it. its just getting too much.everytime we have a family occion he somehow happens to spoil it because of his behaviour.when it was my little girls birthday in march we all went to a kids jungle jims for the day.every child played lovely but my nephew was a knightmare.he started saying swear words in front of everyone,i was mortified.i dont know what to do because my sister is so awkward. and to be honest her idea of discipline is to scream at him and smack him really hard at which he just laughs at.all our family are just sick of his behaviour and worried he is going to get worse as he starts school next year.what can i do? as my sister is not easy to approach about the subject