Everyone is a bender of some kind of element.
"Fire is the element of power. The people of the Fire Nation have desire and will, and the energy and drive to achieve what they want. Earth is the element of substance. The people of the Earth Kingdom are diverse and strong. They are persistent and enduring. Air is the element of freedom. The Air Nomads detached themselves from worldly concerns, and they found peace and freedom. And they apparently had great senses of humor. Water is the element of change. The people of the Water Tribes are capable of adapting to many things. They have a sense of community and love that holds them together through anything." -Wikipedia
Here's who I think would be what.
Kaede: Water bender
Shuichi: earth bender
Maki: Fire bender
Kaito: earth bender
Himiko: air bender
Tenko: earth bender
Gonta: earth/air bender
Miu: air bender
Rantaro: air bender
Tsumgumi: fire bender
Ryoma: water bender (just imagine if all that community and love is taken away)
Kirumi: Earth bender
Angie: Air bender
Kiyo: Water bender
Kiibo: Fire bender (remember the 5th trial?)
Kokichi: Fire/air bender
Yeee let's see what you think bout this list