There are so many types of flatworms and flukes; I sure can't tell. If this thing was on just one fish, I'd call it a generic isopod-type critter and remove it with a tweezers; but more than one says 'worm' of some sort. Prazi-Pro should work. Salifert makes (I think its still around) an excellent flatworm treatment too. If it is a flatworm, there may be a lot more of them. Flatworm killers are generally reef safe; but big flatworm die-offs can be a real problem; there's something that,I'm too lazy to look up, that is toxic in the dead worms.
Unless you're sure that its the same thing on the angler, my first instinct would be to remove the one on the rabbit(?) by hand.
