I am the mother in law and my sons wife is cheating on him.?

My daughter in law is cheating on my son and he is going crazy. My grandkids are being left every night with her mother to sleep on the floor when they have beds at home to sleep in. This situation is driving me in sane. I just want my grandkids to be safe and feel loved and they are not getting that now. What should I do or not do?. Help! This is breaking my heart and my sons. He works off shore and things here at home are just out of control.