If possible, kill one of the queens. Occassionally I see recommendations to
unite and let the bees figure out which will take over the new colony. I've
done this and succeeded, but earlier this season, I united two swarms, and
somehow both queens were lost. If you have difficulty finding the queens,
look for them during a honey flow. I killed two queens for requeening
purposes this weekend, and found them relatively quickly since the foragers
were furiously working the clover and blackberry blooms.