1)
What do we learn from "v'Echav l'Mishpechosav b'Hisyaches"?
1.
Radak: He was Nasi, and also his brothers headed known families. Malbim - b'Hisyaches teaches that this was when their lineage was recorded, in the days of Yarav'am and Yosam (17).
2)
How was Ye'i'el the head?
1.
'Rashi': His primary lineage is in Divrei ha'Yamim of Malchei Yisrael 1 . Ye'i'el and Zecharyahu were the head; the others' lineage was from them.
1
This Sefer discusses Malchei Yehudah; Sefer Melachim is the chronicles of Malchei Yisrael. We do not find Ye'i'el and Zecharyahu there! Perhaps 'Rashi' means that it would have been proper to write them there. (PF)


