Ryumi was originally a cook for a diner, easily prepping food with just her magic. She was also a good fire dancer and a singer. It was then when she saw someone in danger from an intruder on the island and fended them off. She continued these good deeds until the wing council of Tsuno Island approached her and offered her a position as Fire Guardian. And She has kept that position for over 4 years.
Eimi was a Marine Biologist, studying the different creatures of the sea on Tsuno Island. She also loved reading the "Aquabold" Comics (obviously a knock off of Aquaman) which inspired her to control the ocean waves and currents. This earned her a spot as the Water Guardian. Given that she can breathe underwater and has experience of preventing casualties from certain klutzy fire kobolds. she has maintained this position for 15 years.
Shizen surprisingly had 2 jobs. One was for helping build homes for the kobolds with his bare hands with other dragons, and a lifeguard. He was considered a favorite among both jobs. One day, Shizen, in his spare time using his strength and magic makes a huge cabin out of nothing but wood and stone from his village. This served as his home for the rest of his life until the Wing Council notices his work and offered him to be the Earth/Nature Guardian. He had this position for 2 years.
Fuuka only got in because she threatened death to the guardians if she doesn't get what she wants. She also bribed them with a fat stack of cash. Coming from a rich family, Fuuka has only been guardian for 7 months now.
In where they live:
Ryumi lives in a mansion which looks scary from the outside but is livelier and more modern inside. Kobolds are in camps around the Mansion, practicing their magic and learning training from the commanders.
Eimi lives in a royal palace similar to the lost city of Atlantis where mermaid/aquatic kobolds serve her whenever she desires. Eimi however never usually needs help unless it's important things like sending a message or organizing an event.
Shizen lives inside a cabin similar to his old one but much bigger and better. It was basically his own mancave. Other kobolds would visit and play a round of pool, get drunk, arm wrestle, work out, or watch a movie. Basically a mansion like ryumi's but nicer.