Water Worlds Roughly To Scale & Tidal Heating Impacts
previous post with images. Ganymede's blue layer reflects entire ice mantle not water layer based on 200 km depth indicated at wikipedia.
wiki ganymede suggests tectonic activity is due to tidal flexing, but ocean is 200 km deep and due to geothermal heating.
Callisto is not in resonance with the other three moons and does not get much tidal heating which is probably part of the reason it is not significantly diferentiated. It is considered a potentially human habitable world however due to it' much greater distance from Jupiter compared to the others and hence lower radiation.
Regards,
Mark