Hmmmm? What do I do to come off as less tense and more fun?

For some reason I kind of feel very shy whenever I am near my family members, I almost feel like a stranger. I mean my family members are in my opinion, the best, I couldn't ask for a better caring family, but for some reason I feel like I don't belong there. perhaps because I am such a shy person? My family members are really open and have a great sense of humor and are loud, are relaxed, like to live life and have fun (they're from Trinidad and Tobago, duh, fun is in the air there, hehe). However I am the complete opposite whenever I am around them, I try to come out from my shell, but for some reason I can't, so they think I am a very serious person and I don't want them to think that because in reality I am a fun caring person who luvz to laugh, have fun and relaxed (but I come off as being tense whenever i am near them). What can I do to seem less like a nervous wreck? Thnx!