When Pearl said, "Oh honestly, you call everyone a clod." And Peridot responded, "Yes but not everyone has control over all of the armies of Homeworld waiting for the word to shatter me!" It struck me that she said all of the armies. It seems that each Diamond had command over a certain faction of gems as can be inferred by phrases like, "my diamond" and having a certain colour of diamond on most Homeworld outfits. Thus if Yellow diamond has control over all of the armies, is it to be taken as nigh-confirmation that Yellow diamond is the only one left on Homeworld and the others were defeated on Earth? Or does it merely mean that because of their status any of the Diamonds have command over all the armies of Homeworld i.e. Are the Diamonds okay with each other using their resources?

I'm inclined to believe it is the former, there seem to be other implications that Yellow Diamond is the only Diamond left on Homeworld. Further more it seems implied that Yellow Diamond is aware there are Crystal Gems left on Earth, and shows particular interest in it. I wonder if she wants the planet to die, not because of a grudge against the Crystal Gems, but because if the planet dies so will any hope of Blue Diamond and White Diamond regenerating. If they can never return to Homeworld then Yellow Diamond would get to be the undisputed ruler of Homeworld. As I said before she seems to be aware that there are Crystal Gems left on the planet, but if she knew that why wouldn't she tell the rest of Homeworld? Perhaps she withheld much information from them and wants them to believe that Blue Diamond and White Diamond were broken, so that she alone would be the Diamond Authority. I'm confident in that she's the only one remaining, not terribly confident on the rest. Let me know what you think.

TL;DR Yellow diamond is the only Diamond left on Homeworld and wants to keep it that way.