About 4.5 billion years ago when the solar system formed there were a lot of collisions between the existing bodies. One collision formed the Earth moon. A body about the size of Mars slammed into Earth. The giant collision spawned a lot of fragments; they eventually amalgamated to form the Moon. Further out another collision occurred and formed the Pluto-Charon plus two addition small moons system, so the answer to the question is COLLISION of two bodies to end up with 4.

It's not a question of "support". All objects interact gravitationally with all other objects. An object that is less massive than another will tend to orbit it, assuming it has enough velocity not to simply crash into it and not so much that it escapes away. There happen to be three such objects trapped in Pluto's gravitational field. Earth has thousands of objects (all but one of which is human-made).