I guess I might as well put down my theory.
Toshio - Wrath
Yumi - Envy
Taichi - Gluttony
Akane - Lust
Yukitoshi - Greed
Michika - Sloth
Reiji - Pride
Toshio, Yumi, and Taichi's deadly sins have already been revealed. Akane's sin is pretty obvious so far. Yukitoshi, Michika, and Reiji's deadly sins were difficult to pin down. Yukitoshi's sin is greed because he displays an overwhelming obsession with power - he wants control of other people, knows how to manipulate people, and indulges in observing extreme human scenarios. Michika's sin is sloth, which is typically seen as the least damning sin imo; Michika has had little character development and refuses to involve herself with others for good reason. I speculate that she probably witnessed a traumatic event and chose not to give testimony of the event. Reiji's sin is pride. At first I thought Yukitoshi's sin was pride, but Yukitoshi is self-indulgent in his obsession. Reiji is similar in the sense that he's both is charismatic and manipulative; he's a "bitch in sheep's clothing" you might say, because his extreme arrogance can be subtle. He is incredibly selfish, concerned with his ego, and holds "achievements" over people. He believes himself entitled to what he wants and projects himself as the victim. On another note, Pride is arguably the worst deadly sin out of them all.