My only comments would be some general advice. I recommend specifying what type of stone the tablets are made of to give the submission more flavor. Also, aside from replenishing water, it may be useful to explain why ship's would put in to this island, and how often they do so (for instance, the island could be on the the path of a major trade route). Go to Comment
Nicely done. I like the fact that they were given more time to play their music, until the music didn't make them happy any more. This actually fits nicely with a particular world outlook I favor; music has power. Sometimes a lot of power, if the players are good enough. Go to Comment
A rumour of the knights of some powerful king that sleep until danger threatens the kingdom.
The truth is that they were rebels, trying to split the kingdom. Once captured they were put into an enchanted sleep, protected from age and harm, until their aims have been carried out by others in which case they will awaken.
There is a loophole in the spell in that trying to take one of their weapons will also awaken them.