I don't think your Dds are being unreasonable.
But as they are 14 and 15, they need to learn that, as an adult, sometimes you have to be sociable to other people, even when you don't really want to be. You can take this opportunity to remind them, of all the annoying people you have put up with on their behalf, over the years.
My parents always expected us to entertain random children/teens, while they consumed alcohol and had fun socialising with people they wanted to spend time with.
Make it easier for your Dd's, get a new DVD or two, so there is a choice, popcorn, new silly Wii game, teach them card games to help break the ice with each other, play the chocolate game with silly things to dress up in. At 14/15 some people don't have the social skills to put others at their ease and as its for your benefit, not theirs, you need to do some preparation to try and ensure they have a reasonable time as well.
Plus I would offer some bribe as well, as some people have horrid offspring and they are a chore to entertain. 