How can I convince my brother of what his wife is doing behind his back?

[Cwest]

so your all in your 20's you already have at least 2 kids, shes 18ish, she has a incestuous kid and your brothers child, your all opiate addicts who get drunk together, hes gone to prison at least twice in the past 6 months, and she steals and whores herself out? I dont think you wanna hear my opinion.