Any ideas on how to un-stick a seized Celli faucet?

I recently purchased a 3 faucet cobra style Celli tower. It was super cheap so I didn't hesitate. Now that I've got it, I've noticed the faucets aren't working well. Two of three taps are completely seized shut, and the other moves, but not smoothly. Any idea how I can un-stick the seized ones and smooth out the stiff one? I know they're made of chrome plated brass, if that matters. Is there a cleaner I can use the soak them in?

I would give them a good overnight soak in very hot water with PBW or Oxiclean. That should loosen them up to where you can take them apart for a more thorough cleaning. You might want to take this opportunity to replace any O-rings, gaskets etc while you have them apart. Try to avoid using excessive force as you could well break or otherwise damage the faucets.