Lazy son in law

My daughter is so unhappy that I don't know what to do. She had our second Grandson a year ago and we have a 6 year old Grandson as well. Her husband s a very good Father. He has always been extremely lazy around the house which has caused endless rows over the years. Then they have a good talk and he improves for a while then reverts back to type. The problem has been exacerbated since my Daughter went back to work four days a week. Also the baby still doesn't sleep through the night and consequently my poor Daughter is permanently shattered and bad tempered and tearful. She says she hates him at the moment and they are always rowing. Their house isn't big and the six year old is becoming increasingly withdrawn and tearful. He is a sensitive child anyway. Myself and the other in laws have the children occasionally at weekends to give them a break, but they tend to go out in a crowd so it's not really 'sort it out' time together. I know I can't interfere in their marriage but am terrified that they will separate. Any thoughts would be much appreciated!