1)
Why does the Torah list Er and Onan, who died in Eretz Kena'an (as the Torah itself states)?
1.
Ramban (in Pasuk 2): This has to do with Gilgul (reincarnation) - which the Ramban consistently refers to in vague terms. 1
2.
The Torah lists all the children of the Shevatim, the vast majority of whom were born in Eretz Cana?an and were therefore included in the seventy souls who went down to Egypt. And it duly explains why Er and Onan are precluded from the list. 2
2)
Why does the Torah fail to list the sons of Shelah and Zerach?
1.
Targum Yonasan: Because all of their children were born in Egypt.
