If they already have cds and tapes as well as the player it may be worth looking through the tracks and using them for some dances (their favourites). Some of the Playford dances may not work on a melodeon, and anyway if you are calling an unfamiliar dance it may be worth learning one thing at a time, then if they like the dance the tune will be in your head ( I find it easier to learn tunes if I can sing them rather than sight read the dots).
I'll pm you the Tom Cook version of the Playford dance Jamaica. It's a simple 4 couple dance, nice pattern and not too energetic.