Yes, I have seen plenty male cheaters. That's why I started trying to think of shows I have seen with female cheaters, mind you trying to recall everything that happened in every drama I have watched is getting more difficult.
As far as the sibling thing is concerned, I know of a few and I will check out the ones suggested.
Any series where the siblings know about each other, but haven't really interacted is welcomed as well. For instance, Doctors.
There is a series where I remember the mother coming to the daughter for money, and you only find out later that she has another daughter and the money is for her treatment. I can't remember what the series was though.