Wow, no idea where Tenzin as an N came from. He has shown to be quite rigid and feeling a powerful need to uphold traditions. He has virtually no spiritual side. I'm 100% on him bring ISTJ.
Korra - ESTP - obvious
Mako - IsTJ - He's the stereotypical "protector," but N/S isn't clear imo.
Bolin - ESFP
Asami - IsFj? - She's hard to type...
Tenzin - ISTJ - obvious
Bumi - ENTP
Kya - ISFP - Fi everywhere
Lin - ISTJ
Jinora - INFJ
Ikki - EsFP
Meelo - ENTJ - I just know Meelo is going to grow up and become some sort of insane dictator.

Varrick - ENTP - He makes a great use of both Ne and Ni all around (the ultra intuitor of the show, makes me want to type him NeNi), but I think his lack of Te is what makes him ENTP.
Zhu Li - InTJ
Amon - INFJ
Unalaq - LAME, some sort of controlling Fe (enFJ)
Zaheer - INtP
Kuvira - something with Te? ENTJ?
Tonraq - iSTP
From left to right
Korra - ISFP, easy to get angry
Asami - ISTJ, industrialist and an engineer, ex-lover with Mako
Bolin - ENFP, Mako's brother, naive and good-hearted, can deal a punch when he needs to, having difficulty typing him, he's not as aggressive as Korra but not exactly as Bumi either.
Mako - ISFJ, Korra's boyfriend and a detective in Police Dept
Tenzin - ISFJ, resents that he's not as connected to the spirit realm as his father
Lin Beifong - ISTJ, police chief, ex-lovers with Tenzin
Amon - ISTP, the bad guy with a distaste for benders
Varrick - ENTP, Entrepreneur, reminds me of Tony Stark
Opal Beifong - ISFJ, becomes an airbender
Suyin Beifong - ISFP, Lin's younger sister, personality is said to resemble their mother Toph, and contrasts with Lin's uptight personality.
Zhu-li - INTJ, Varrick's assistant, marries to Varrick and becomes 2nd president of the league of nations
Bumi - ESFP, Tenzin's older brother, eccentric guy, happy-go-lucky, his bio says though he lacks bending, he's physically much more able than he's portrayed in the series, he might be similar to a younger Uncle Iroh in the previous series.
Kya - ENFJ, Tenzin's older sister, teases him for being sensitive
Kuvira - ESTJ, military commander with a desire to conquer the nations to build a one nation world state.
Zaheer - ESTP, anarchist tendencies with desire to incite chaos to enable the strong to rise. Zaheer is a staunch anarchist who sees chaos as the only acceptable world order. He is willing to destroy anyone who stands against him and resorts to extreme measures in his campaign to eliminate the governments of the world. Master airbender.
Unalag - ENTJ, conspired to reorder the world according to his ideal, spiritually strong
Meelo - ESFP, Tenzin youngest child
Ikki - ISFP, Tenzin's mid child
Jinora - INFJ, Tenzin's eldest child, Jinora is a quietly reserved, intelligent, studious girl, much different from her younger, more rambunctious siblings. Out of Tenzin and Pema's four children, she is the calmest and most mature. She has a natural connection to the spirit world.
Prince Wu - INFP, vain and inept aristocrat, head in clouds.
Characters not in the collage
P'li - ESTP, Zaheer's gang member, can shoot explosive beams from an eye on her forehead
Migh Hua - ESTP, Zaheer's gang member, master water-bender
Ghazan - ESTP, Zaheer's gang member, master lava-bender
Tonraq - ESTP, water tribe leader, older brother of Unalaq
Bataar Jr. - INFP, naive idealist, Kuvira's lover and loyal follower, Suyin's son
Pema - ISFJ, Tenzin's wife