Ganymede has a thick water mantle which may have behaved like the Earth's mantle, breaking the crust and moving the pieces around. Ganymede's crust thickened more slowly than Callisto's. Ganymede is slightly larger than Callisto and would retain more heat. Active geology persisted for the first billion years until the crust thickened to the point that it could no longer be fractured through to the water mantle. A satellite completely covered with a frozen ocean 100 kilometers thick.
Few craters are visible on Europa.
Europa must occasionally be resurfaced by tidal warming of its global ocean. Conditions under the ice crust of Europa may be suitable for sustaining life. Io's orbit is not perfectly circular due to the gravitational tugs it receives from the other large satellites. The non-circular orbit produces tidal squashing which heats the interior. This heating drives active global volcanism.