I'd recommend the 12-24 for the banquet room interior, and also recommend shooting it as close to dawn or dusk as the setup will allow, so the interior lights are balanced by what's outside. Might not look like lunchtime at the clubhouse, but very sexy for architectural interiors with a view... and bring a solid tripod and a remote shutter release (cable or IR).
The 15mm prime is also a good choice for tight interiors like a locker room (not sure what you want to show, though). Maybe go for a very high angle (standing on a bench or something) to see if you can get more of the amenities and less of the plumbing under the sinks, etc.
Finally, for your lighting, that is an art form unto itself.
Read some of this stuff from The Strobist for hints on what to do with minimal off-camera flashes. And/or really consider auto-exposure bracketing a few stops apart and combining them afterwards in a dedicated HDR and blending program like
Photomatix. Even if you shoot handheld (really, you should use a tripod!), Photomatix can align the images for you if they are close enough.
Finally, I shoot hundreds of interiors a year, but they are of the most boring, featureless spaces you can imagine: film studios. Even so, it takes me a bit of walking around the space to get an idea what would show it off best of all...