25th Anniversary Party

Hi everyone,
In about six weeks I will be hosting a surprise 25th wedding anniversary party for my parents. Although I`ve hosted small parties before, the catch of this event is that it will be at a restaurant. I expect anywhere from 12 to 20 guests, including my folks.

The party itself is not the only surprise aspect of this event. My younger brother will be flying in from college and surprising our parents at the restaurant the day of the party. The biggest surprise, and the reason I`m on a tighter budget than I`d hoped, is that my brother and I saved our money and haved booked a two-week European vacation for our parents. (We will be surprising them with this information at the party.) That said, money is now sort of a problem.

At the moment, my main concern is the payment issue. Some of my guests, my grandmothers and adolescent cousins, for example, will not be able to afford to pay for their own meals (we live in NYC, so nothing is cheap). Other guests, friends of my parents (with jobs, of course) will. Since the restaurant I chose will probably not have a pre-fixed menu, how do I get around the problem of some guests paying and others not. Should I say this in advance, or just hope that people assume that since my brother and I are so young we can`t exactly foot the bill. And what do I say if someone asks, or if I think that the money is an issue and they won`t come because of it?
Any advice would be greatly appreciated.
Thanks,
Rocio