I can only imagine that his wives were jealous of the other at times. He went away for some time and while he was gone, the wives decided to get ready for him by going fishing and getting some fish to cook. The elder wife went first. The younger wife went second and her son was brighter than the elderly wife's son.
That made the elderly wife jealous and she sharpened a razor throughout the day. She planned on using the razor to kill the young wife's son while the boys slept.
She killed the boy while they were sleeping and the next morning when she went to move the body she realized that she killed the wrong boy and she killed her son.
When she realized it was her son, she took him and ran into the forest. When the husband got home and found her missing he went to go look for her in the forest and they found her and killed her too.
Bibliography: The Jealous Wife by Notes on the Folklore of the Fjort by Richard Edward Dennett