Weight obsessed relatives, almost crazy?

Well, here's the thing. I have 1 aunt who has 1 husband and they've got 2 kids who are my cousins. The whole family is weight obsessed. What bothers me the most is that it's affecting their children the most. The kids are 11 and 9 years old. The whole family is fat, I'm not trying to sound rude, I love them with all my heart, but this is crazy. They've got scales all over the house, wii fit, this push up machine, a tread mile, a trampoline. Like yesterday it was my birthday, and the little 9 year old boy (my cousin) had a lot of cake, a lot of ice cream, then he was like "Mom, I've lost 0.3 kg/ half of a pound" then when I suggested we'd go out and play on the playground or something his big sister said "Yeahh, you need some exercise" and when we were climbing on these ropes he was like "Hurry up fatty" to his sister. Then when he got tired after about 1 hour his sister was like "see, all you do is sit down and eat, get up and keep walking" and his sister said to me "you're so skinny, how much do you weigh?" and then he asked the same question about 10 minutes later and I told him, and he said "Then I weigh less than you!" and I said "Yeah you do, but I am much taller" then he told me to go over to this thing that looks like a balance scale, but on the playground, and then of course I weighed more, then his sister came up and she was like "Yeah, we're fatter than you" This was not how I visualized my birthday, and I seriously feel sympathy for them, when I was their age I never thought about weight & stuff like that. What can I do to help them?