The first impression you get from these guys is that they're a bunch of bumbling clowns. How they even got this far on the Grand Line is anybody's guess. Their leader can't lead, so nobody knows what to do in battle.
The one thing you do notice, is a sure sense of teamwork. These guys are a family, and anybody who's met them would tell you the same.
Despite the rather silly first impression most other pirates get when meeting them, they're really a serious bunch. The most vocal of the group is Nial , and the others just follow her. It just happens to be that Nial is also goddamned insane...and 15 years old.
The Burning Aces Pirates come from the now destroyed Dozei Island, where they helped save the day and yet wreak horrible havok at the same time. It's a matter of debate whether they were exiled from the island or simply left when they were no longer needed.
In the past, they were part of the task force on Dozei Island that faught the ancient evil of the IZ, who were the likely cause of the island's eventual demise. There, they were made famous by tales of their exploits, one of which is reported to be crashing a World Noble's airship straight into a broken gate to force it open, or destroy an ancient monster (nobody's got the story straight). Nial will tell you that all of it is true. Whether that's what happened or not, is only known to them.