What am I doing wrong?

Ok so my husband and I have been married since August 08 and its been amazing with him. We met in April 08 and knew it was love. Anyways, his sisters act really nice to me over the phone and things but when I met them in person they were snooty to me and talked bad about me behind my back. Honestly? Come on now. I'm 20 and they are 26 and 30. I met them when we were just dating and they still talk crap even now that were married. Like saying I won't be around for long and that he should still be with Kayla (their best friend, who he pity f**ked). And they say I'm using him for his money..... He's a Marine....he doesn't have money. When I met him he was a grand in the hole. but they just don't get this. They have only met me twice but insist they "know me" it just really bothers me because I love him with my entire being, I pretty much wait on him hand and foot and he is just my world. But they don't see that because they live so far away. Well I guess my questions are, am I doing something wrong? And How can I confront them about it and make them see who I am without a huge argument?