Why would you still say that you believe the crystals are siphoning mana from people when it was just established that they aren't? The dragons are the only source of mana on the island, which means either there's a lot of them, they have a lot of mana, or both. It's entirely possible that they have people whose job it is to charge the island's core, some kind of monthly/seasonal/annual/whatever ritual where they do it as a community, or something else to that effect.
That the airship and floating island cores are both the same kind and 'guided' by the moons points, in my opinion, to some kind of magic magnetism. This also means that the moons, or whichever one(s) is(are) controlling these things are full of a specific kind of mana. One thing we can try is to get smaller rocks and charge them up and see if we can get them to move each other.
RH: Eyes peeled and heads on a swivel, Shrikes.
MA: Have I mentioned that I hate fire?
Kale'shido- I would've gone to the Sarghress, like the other exiles, but I fear for my family's safety as much as my friends'.