Could a breath player be able to start fires too, or at least keep them chugging because fire needs oxygen to thrive. If it is that they could only keep them chugging, consider: a doom and breath duo that just goes and fucks shit up

A Doom-Breath Duo could definitely do that. The Breath Player alone, starting Fires, I’m not quite sure, but DEFINITELY fanning them as well as extinguishing them, that’s like, part of John’s little inscription, remember?

They wait for he who would extinguish candles whilst fanning a fire. 

Breath IS Wind and Air after all, so all that has to do with wind blowing, Breath Players should be able to do.