Given the many possible histories your wife could have had, I consider your situation to overall be a net win.
-She's only fucked two other guys. This ALONE makes the fact that she was fucking her brother for one of those guys worth it. A body count of two before you is practically a fucking unicorn these days. For me, anything under 20 and i'm like "cool, she isn't that much of a whore."
-Second, and don't underestimate the importance of this, if she was fucking a stereotypical Chad, the best case scenario is that it's her brother. Seriously. That's about the only possible Chad from her past that i'm pretty sure she wouldn't cheat on you with given the chance. Murderer, Rapist, Drug Dealer, Pimp...all those guys would definitely still gve her the tingles. You'd be one bad fight or horny day for her away from her hopping back on his dick if it weren't her brother.