Is Rengar from the same place as the two new champions or no?

If you think about it: No. It would make sense at first glance, but if I recall correctly, Rengar was found and raised on literally the opposite end of the world in a jungle. He also feels different (Rengar: Predatory These things: Edgy and confusing faeries

Yes. In their voicelines, they refer to him as a Vastaya. Most likely he was born there, but migrated to the Kumungu Jungle to pursue stronger beasts.

He is a Vastaya with currently unknown birthplace....stay tuned for Rengar lore update.