I really feel for you Bob, I get the same from my mum quite a bit. She has been on seperate two week trips to Florida with me and my sister. When she took my sister (plus BIL and their 1yr old daughter), sis and her family didn't pay a penny. Flights, hotel, park tickets - the works, mum paid for it all. When she took me and Scott, we didn't get so much as a burger at McDonalds off her despite us booking the entire thing and suprising her with breakfast at Chef Mickeys.
Then, that Christmas (a few weeks after we got home) she decided to buy a new massive TV, about 39" flatscreen, very expensive. When she bought it, she added a second one and gave it to my sister. That really hurt.
It can be really hard when your parents act like this because when you tell anyone you sound like a spoiled 14yr old "my sister got a TV, why can't I have a TV too? MUUUUUM!!" but it's still kinda unfair. Just *** my sister has very little self control financially (a classic example would be when we all went out for lunch, sis spent the walk listing all the gigs she was going to soon, then got mum to pay for her daughter's lunch *** she couldn't afford the £2.99 kids meal) doesn't mean she deserves all this stuff.
Your cosuin sounds like a spoilt child in the body of an adult, he's been able to stay that way just because he's always been allowed to have whatever he wants. Really gets my goat.
Sorry, I'll stop ranting now.