normal 11 years old behavior

I spent a whole week vacation with my boyfriend and his 2 children and it was a nightmare when my boyfriend 11 years old son who is consistently complaining, demanding, manipulative and totally controlling to his younger sister. It seems like he only wanted to do thing in his way which my boyfriend (his father) most of the time following his son request but if he doesn't get what he wanted, he always make sure that his sister have to be suffer as well. He nagging her, make her feel small, pushing her or hitting her. It seems to bothering him so much if his sister seems to having a good time or doesn't mind what is going on.
    Couple days ago, everyone decided to go out for ice cream but the boy doesn't wanted to, anyhow his father told him to come out anyway so he came with us and got an ice cream then we all decided to sit down and finished our ice cream but the boy doesn't want to sit down, he walked away to sit in the car by himself..his father doesn't do anything about it. When we all went back to the car he started to nag his sister, they got in a fight and he finally hit her. His father told him to stop but he doesn't so his father raise his voice couple times until the boy stop. When we got to our hotel, right after the car stop the boy open the door and ran away into the wood near by. My boyfriend then follow him after ~ 15 minutes they walked back and again his father speaks very softly to him and seems to pampering his son. When his daughter came close to his son, he then firmly said to his daughter to go away and don't go close to the boy.  
     I think that's not right, his father should sit down and talk to him that running away is not the right way and the father should have some consequences for those kind of behavior. I don't know what to do exactly, I don't think that I'm in the position to say too much but I don't like what's going on in this family at all. And I do want to help but also doesn't want to get into trouble, though I told my boyfriend that they should sit down and have a serious conversation (a father and both children) my boyfriend should tell them what's his expectation and if anyone misbehaving they will be a consequences for it...but what's kind of consequences?? what should you expect from a 11 years old boy and a 9 years old girl? help please!!! I know whatever that his father (my boyfriend) doing with his son is doesn't work and thing will get worse if he doesn't find an effective way to discipline his son. Can you tell me what should I do in my position and what should my boyfriend do to discipline his son, what's kind of consequences that appropriate for this age?
    

[margypops]

I dont think you are in the position yet to tell your Boyfriend how to behave with his Son, it may allienate you, You are correct this boy needs some firm talking to and told the limits of his behavior.it is his Dad or Mom if shes around who can do that, Perhaps see outside the obvious for a minute , he is obviously Jealous of his Dads attention to you and is acting out., maybe hes not always like that and he was showing you he gets his own way, also Dad probably didnt want to be -little him in front of you. If the subject of the children comes up you could carefully express how it surprised you the Boy was unkind to the girl., it could lead you into a discussion and he may ask your advice.From your post I would say you have a lot of incite and would be a help.Good Luck, let us know how you get on.