What do you think about me cheating on my wife with her daughter?
Why did you cheat with her daughter?
I know she's having an affair as well.
This is messy situation made worse. Sleeping with her daughter only complicates things. You need to deal with your wife first.
I can't tell her about it, my wife will kill me for sure. It's safe.
Talk to your wife about her cheating and discontinue the inappropriate relationship with her daughter. You need to figure out whether you your relationship with her is repairable and then act accordingly.