Master Ekul, I'm not sure Zez-Kai and Zhen-Kai are two different persons, but I can tell you they both have existed. As is the case when it comes to Kadaj and Kadja, Kadaj was a Padawan of Master Menelaos and Master Xzar-Bin, and Kadja a Padawan of Master Shin.
Thank you all for your contribution, I will be updating the tree soon.