I know about the jealousy, I can still remember when my father first married my stepmother and I'd literally get inbetween them when my father would get home at the end of the day :-) My father was gone for 8 months in the service (1957 :-) and it's very hard; I have 3 brothers and a stepsister.

Married folk need a separate time. It's almost as hard for them as for kids. Sounds like your Dad is spread kind of thin financially with all the children to take care of in two marriages. I think you only get one or the other of your things to do. I went to Europe my senior year and had to trade my stepmother the promise that I would get a job in the summer. Your father is probably paying as much as he can afford, helping pay for your food and mortgage and stuff so your mother can afford your trip to Europe. Are there multiple sessions at camp? Maybe you can get a job before or after to pay for it? Borrow from your sisters' and pay them back in services or something?