About Tenzen:
Can he truly be a past us? We know that there is only one soul of us on the source and the rest is on the shards. He cant be us imo because his soul was still with the dragon when it was released, so we never would have been reborn thanks to that. Or he had to be only a small part of his soul still lingering but why would that be when he seemingly sealed his aether with it?
About Varis:
I think there is a very big chance that he was the one that ordered the use of the black rose in the future we changed. We would have never went to the first thus Zenos and other characters would probably not be were they are right now and with our power we surely would have changed the battle more towards Eorzea thus Garlemald using the chemical weapon sooner.
Varis was ready to slay all beast tribes (genocide ftw), raised the monster that was Zenos, worked together with Elidibus even after all the talk about "humanity making their own destiny", was ready to destroy all shards and rejoin them because he wanted to be a perfect being (which I doubt he would even be part of since he is seemingly missing the echo) and for that was ready to bring huge calamities onto the source..he also had his moment were he showed his evil face including the evil aura..some hoped that this was Solus but we know now that Solus was not there anymore and that this was truly Varis. So yeah him ordering the use of Black Rose makes the most sense..so he kinda did use genocide and killed a lot of his own people with it. He is a villian to the end and I see it quite fitting that he dies through the hand of his son even if I still wished that Zenos would not play any big role in the future arcs..