I mean.... their elements are honestly pretty easy to guess from appearances, despite not necessarily tying directly into their powers but...
Rekki is fire. She's hot-headed, impetuous and destructive, but also passionate, warm, brings out the best in others and is always ready to fight off monsters.
Subo is earth. He's calm, worldly, practical and nurturing. He's also quite lazy and passive, or even actively cowardly and a bit hedonistic.
Sarin is water. Deep-thinking and serious, her cool, collected exterior hides intense passion. She will tear you to pieces with cold, unrelenting intensity. Prone to overthinking or hesitating and letting others make hard decisions for her while she agonises over ideological purity.
Urien is light or lightning. He's a quick-thinking opportunist who sees himself as a lofty and important person, better than others. He's attractive and charismatic, but like light or lightning, he's actually quite destructive, especially when given power, and can be misleading or dazzling.
Urien's sister, Jules is his opposite. Darkness. Bewilderingly odd, quiet, gloomy, hard to understand and nowhere near as shiny or charismatic as her brother.... But is darkness really all that bad?