Nimrah may have been angry at the treatment of his brother, but he may also have had a healthy sense of self-preservation. If his father had killed his brother, his father could kill him. He gathers what support he can and goes to the land where Omer is dwelling with his kin. No doubt he intended to join forces and create a better defensive position that the two groups could do separately. In spite of his father, Nimrah was the great-grandson of Omer through his mother the daughter of Jared who was the son of Omer.