1)
Was Yizrachyah the only son of Uzi?
1.
Malbim: The others were not mentioned, for they were under the Beis Av of Uzi.
2)
Four sons of Yizrachyah are listed. How were there five Roshim?
1.
Malbim: He had also other sons. Yizrachyah was considered a Beis Av of his remaining sons.
