The New Girl likes me, her brother doesn't want her seeing me. Long story.. but help!?

So I go to a University, still live at home with my Mom and Dad (I'm only 19). We live in a nice neighborhood, and anyways our old neighbors who were slobs moved out last Winter and around January this family from Inagi, Tokyo Japan moved in. There was a brother (22) and sister (19), and their parents. Nice family, but the brother seems to be very protective of his younger sister. Anyways, the brother has a cl with me and everything was going great, we became really good friends and when I went over to his house to play some video games, I saw her. She was really quiet and spoke very little English. She brought us some drinks then left really quick. Later I found out she goes to school as well. When I saw her, she was with her fellow Japanese friends and I waved hi, and she kinda smiled and her and one of her friends just looked at me and giggled. Later that day I was heading towards my car, and she approached me and said hi. I tried talking to her more, but she mumbled something and left. Later when I was at their house working with the brother (we're lab partners), we took a break and he needed to grab something from another friends house so he said he was going to be back in a little and for me to make myself comfortable. Well his sister came in his room and saw me. I was playing Black Ops and she said if she can join. So we played for awhile, and her brother walked in and said something and she said something back and he looked at her sternly and she left. He apologized if his sister was being annoying but I said she was fine. Well later, for 2 months, she has been studying English like crazy, the brother now has a girlfriend and one day she asked if me and her can hang out and I said sure. So we made a plan for a Friday. We were watching an Anime movie called Princess Mononoke, my family was out, and during the middle of the movie, she laid her head on my shoulder and I wrapped my arm around her and she looked up at me and turned beet red. Well we were interrupted by some knocking on the door, and well I answered it and it was her brother, he asked if she was there and I said yes. He barged in and grabbed her and stormed off. He kinda glared at me and left. Later on Facebook, I got a friend request from her (being mutual friends of the brother). I accepted it and we started to talk. We talked about what happened, and she said her brother was just trying to protect her. I said it was okay to not worry about it. The next day my friend asked me if anything happened between me and his sister, I said no, and he said for next time to ask for his permission, since its an older brother- younger sister rule. Well I found out every time I asked to hang out with her, he said she was busy with her studies. She one day approached me and asked why I haven't called her. I told her what was up and she just got angry and said that she's an adult and she hates her brother for doing what he's been doing since she was 16 (when she was allowed to start seeing boys). Well I was invited over with a couple of other guys over to my neighbors to have a game night, and had a blast. Well it was a night over, and when everyone was asleep and I was getting a drink of water, I felt arms wrap around my waste and I turned around and it was her. She was blushing and I stroked her hair to the side and we kissed. In the morning we were having breakfast the bunch of us, and she was sitting infront of me. The guys were talking about how awesome last night was with all the kills we got online, but I was staring at her and she was smiling at me. The brother noticed and told her that their parents asked her to go get some bread. Later at home I got a message from him asking why I didn't tell him about me and his sister, and I replied it happened recently. He said to me that he wishes I would reconsider about going out with his sister, and I told him that his sister is a very beautiful young girl and that I like her too, and I asked him if I could date her. He told me no, that he doesn't approve. Well when I showed her the message, her and him gotten into a huge argument. The next day she wanted to go out, so we did and we saw Thor. When coming back, he was waiting for us. He yelled at her and told her to go inside, and he started yelling at me. He said that we were good friends, and why was I going against the one thing he asked of me. I told him that me and her really like each other, so why can't he be happy for us. He said that American men are only after , and I told him that I wasn't, that I would never disrespect his sister. He just said forget it and left. Now he's not as friendly, we still hang out, but it wasn't as before. His sister and I have been coming closer and closer, and their parents and my parents are good friends and are glad for us... but why isn't he happy that at least his sister is dating someone he knows and is friends with?