Boyfriends brothers girlfriend.

Ok so my boyfriend of 10 months brother has been dating this girl for almost 2 years, and no matter what I do with them and their family she always seems to be there, she goes on vacations and everything with them and I feel kind of rejected. She's taller and skinnier than me and I get very insecure when I'm around her, I just don't really know how to deal with it because, I love my boyfriends family and being around them, but I don't feel half as included as she is. What do I do?