Depending on the number of people, I'm not sure about the power of the pop-up flash. If you could get your hands on a external flash or two, you'd be a lot better. Usually, indoor lighting is just weak and strong enough to give you a mis-match with the flash. If the flash is too weak to overpower the existing light, then It's very difficult to post process to get nice flesh tones.
If the ceiling is low and white enough, the use of an enough powerful external flash is the key to success for group shots.
If you don't have one and can't rent of borrow, then I'd go with the available light and crank up the iso.
Let us know how it turns out and share your pics.