Vayigash: Yaakov's "Sons" Hetzron and Hamul

Parashat Vayechi is filled with family reunions, love within family, loss within family, trying to move on from loss, beginning from a seemingly minor point and getting to a point of greater significance. There is one pasuk describing Yehuda's "five" sons, mentioning the death of Er and Onan, and saying that the sons of Peretz are Hetzron and Hamul. We analyze this section in the midst of the list of Yaakov's 70 children. Why are Hetzron and Hamul here? Do they posthumously replace Er and Onan?  Through our investigation, we gain perspective on Tamar's actions, as well.