In that case, it'd probably be best to make the Ash user and the Lime user the same person(and out only Ash user also used Lime so it works) and have the third member be the descendant of Son Goku's jinchuriki who uses actual LAva(since I'm pretty sure Son Goku is the only one who uses actual lava.)

Senko's interest in the Chunin exam would consist entirely of opportunities to gather samples for research.

Villages usually only send their best to the Host village=better odds of a lot of shinobi with unique abilities that may or may not have a genetic factor she can study.

...Senko and Yuyuyu collaborate and they invent the Ninja Info cards?