someone please help me

The other night, my sister was sleeping with my mom because she was scared of the storm that was going on. She told me the next morning that my mom was sending nudes/risqué pictures to someone, who WASNT my dad. We knew it wasn't him for sure because he was asleep and he's away for work. I looked into it, and it's true. I have the guys Facebook and I screenshotted most of the messages going back and forth between the two of them (the ones that concerned me).