I'm confused by the amount of Qin Xians. Like, how do I understand which is which?

There's Qin xian from the first world that's currently "possessing" the Qin Xian/Wang Yi's master from the current world, then the Qin Xian from the zombie world, then X from the scientificy world, and lastly probably the first Qin Xian from when Wang Yi was still a system