Sforno on Exodus 6:14/ספורנו על שמות ו׳:י״ד

1אלה ראשי בית אבותם, Moses and Aaron were justifiably referred to as the heads of the various tribal groups of Israel, as they were the most respected and most honoured. ראובן בכור ישראל, seeing that none of his descendants were particularly noteworthy except his sons who had been part of the original 70 persons who had come to the land of Egypt from Canaan, none other are mentioned. All those 70 persons had already died as we know from Exodus 1,6. The same consideration held true for the descendants of Shimon. On the other hand, Levi, the longest surviving member of the original 70 Hebrews who migrated to Egypt, managed to raise even his grandchildren to become leaders of the people in their own right. Amram produced three outstanding children in the persons of Aaron, Moses and Miriam, all of whom attained prophetic stature. Aaron married a sister of Nachshon who had been considered the most notable member of the nation in his time. He begat leaders of the generation who were later on appointed as priests. Eleazar, son of Aaron took as a wife one of the daughters of Putiel who was also considered outstanding in his generation (compare Nachmanides). This union produced Pinchas who was granted a covenant of “peace” by G’d as a reward for spontaneously slaying a high ranking Israelite prince who flagrantly engaged in forbidden sex with a Midianite princess and had challenged Moses to do something about it. (Numbers 25,12) אלה ראשי אבות הלוים, just to tell us that Moses and Aaron were the respective heads of the Levites.