Speaker placement

[RIKKI TIKKI]

I would think that most of your attention should be directed to the Karaoke (80%), and then try to enhance the music coming to the dance floor (20%)... Using only the two speakers that you now have, something will have to be sacrificed in the way the sound is projected to both areas... in relation to the stage and dancefloor, where are you planning to set-up your Karaoke station?
Try putting one speaker ( you have stands I presume ) in left corner behind the stage / left, and the other behind the dance floor / right corner... do a sound check with a friend that can give you a second opinion on the mix... luckily with a somewhat older crowd you won't have to pump out any extra bass on the dance floor... or I would recommend another woofer in the center or stage / right... if you can afford an extra speaker, consider using one (Monitor) in front of singer for their benefit...

Good Luck and Have Fun! Your enthusiasm will come through, and make your show a success!