What is the significance of the words "Ka'asher Tzivam"? What exactly did Ya'akov command them before his death regarding the transportation of his coffin?
Rashi (on Pasuk 13): He commanded them a. that only his sons (and not his grandsons, whose mothers 1 were Kena'aniyos 2 ) should carry his coffin, b. the exact position where each son was to stand by the coffin, 3 and c. that Efrayim and Menasheh were to replace Levi 4 (who was destined to carry the Aron ha'Kodesh) and Yosef (who was a king).
Moshav Zekenim, Hadar Zekenim: According to the opinion that the Shevatim married twin sisters from other mothers, they were not Kena'aniyos! According to all, we can ask from Sha'ul ben ha'Kena'anis, i.e. Ben Dinah! Yakov did not want to arouse jealousy [and forbade all grandsons]. Moshav Zekenim - however, Rashi says that Efrayim and Menasheh carried!
Hadar Zekenim, Riva (13), from Pesachim 50a: How could they marry Kena'aniyos, which Avraham was so adamant about? Kena'ani is a merchant. Riva - the Gemara said so only about Yehudah, who was king over his brothers.
In the same formation that they would later camp around the Mishkan in the Midbar (as the Torah describes in Beha'aloscha). Bamidbar Rabah (2,8, partially brought in Rashi Bamidbar 2:2) - Moshe was concerned lest the Shevatim object to the directions in which Hashem commanded each Shevet to camp. Hashem answered that they have a tradition from how they carried Yakov.
Riva (13), Moshav Zekenim: Moshe carried Yosef's coffin, even though he was a Levi! Yosef's coffin carried itself - "Noheg ka'Tzon Yosef."