I think that Chris K's advice is spot-on, but I would leaven it just a bit. Take charge, but take charge of the _dancing_, not of the music. Don't try to tell musicians what to play or how to play it when you don't know what you are talking about. But you DO know what you are talking about with dancing, and approach it from that perspective: This is what I need for the dancing to be successful: no vocals, a constant tempo, play until I tell you to stop, etc. If you respect their area of expertise, they will respect yours.
I would be wary of providing sheet music; even if you give them the
perfect tune, what they will play may sound nothing like what you are
expecting. I've learned from experience that even when a band knows a
specific tune, you may still be very surprised by what you get.
Definitely try to get there very early and talk with the musicians. Find out what they are comfortable doing, then modify whatever you do to fit in with that. (I agree with Chris, from your description, the chances they play any jigs are pretty minimal). Be ready with dances that do not need standard-length As and Bs to work, e.g. the paddle dance, Edinburgh Rock, a grand march.
Another reason to get there early is to figure out what the sound setup for this gig is. Are you using a band mic? Are they expecting you to work from the floor without a microphone? etc.
St Paul, MN