Hi,
As you can imagine Elba is in the middle of peek season so finding 3 rooms for one night will be virtually impossible. Have you tried the hotels in Piombino? They could sleep there Saturday night and take an early ferry sunday morning. They would be able to see quite a lot in one day and Elba is really lovely so it would be a shame for them to miss out! Best of luck and hopefully we'll see you're group of 8 enjoying themselves on one of our beautiful beaches tomorrow.
Gentile sig.Gimmi Ori