Yeah, people figured that out a long time ago. Jasper revealing she reports to yellow diamond confirmed that the diamon overlords are the ones in charge.

 If you watch serious steven, you can see a mural

 of what might be the temple fusions hands grasping for white diamond while she retreats into her gem. The gem that is found within the pyramid ship.

There’s also a mural of rose fighting blue diamond and blue diamond seems to have the power to shoot solid objects. Kinda like the blue gem found in the lighthouse later on. It’s possible that blue diamond was defeated and sealed in the lighthouse.

Last, there is the mural of yellow diamond not really doing anything other than looking pissed. Yellow diamond is the only one confirmed to be on homeworld.

Also, the symbol of of the diamonds seem to be triangles

You wanna know who else had a triangle symbol?

Rose did.

now, with all of the theories I have seen, I have come to the conclusion that

1. white diamond is currently in the gem temple
2. rose was a diamond
3. blue diamond might also be in the gem temple
4. yellow diamond is the last diamond overlord
5. lapis was forced into the mirror at the start of the second gem war for earth, Blue diamonds invasion.
6. greg was most certainly there for at least the second gem war.