Chronology and other relevant information
I read it at the latest in the mid 90s, which means it would most likely written before that. I remember multiple books, none particularly large.
It involved the main protagonist who initially discovers he has the power to control fire (Which is rare but not impossible - someone refers to him as a "Firebrand") but eventually discovers he has more broad elemental powers which was either unique or at least ultra rare.
He gets together with other people with these powers to overthrow some sort of evil.
I think one of his companions had some control over poison.