Hello and thank you for posting your question to Brainmass.
Probably not. Jupiter planets are too small and too far away from each other to make them collide and form a new planet.
The moons (of any planet) move in a gravitational potential "well" which is exerted by the massive planet. The planet pulls the moons in while the moons velocities are enough as to not let the moons fall into the planet.
Thin about the moons as a cannon ball shot from cannon on earth. The cannon ball exhibits free fall acceleration (due to earth's pull) but since it has enough speed it doesn't fall straight down, but ...