Why does the Torah list the sons of Amram, Yitzhar and Uziel, but not those of their brother Chevron, who had sons, since it says in Bamidbar, 3:27 "u'Mishpachas ha'Chevroni"!
Moshav Zekenim: Likewise, it does not name here the sons of Isamar (Rashbam) or Moshe (Hadar Zekenim), or the grandsons of Gershon and Merari (Da'as Zekenim, on Pasuk 21). 1
Da'as Zekenim (on Pasuk 21): He did not have sons. 2
Why does the Torah tell us how long K'has lived?
Rashi: It teaches that the four hundred years decreed at the B'ris Bein ha'Besarim were not all in Egypt, seeing as K'has went down to Egypt, and if we add all his years, those of Amram and the eighty of Moshe, we do not reach four hundred. Therefore we must say that they are counted from Yitzchak's birth.