Or HaChaim on Numbers 18:1/אור החיים על במדבר י״ח:א׳

1 אתה ובניך ובית אביך, "you and your sons, and your father's family." I believe the words ובית אביך refer to Moses, who was also a descendant of Aaron's father, to warn him to observe all the strictures i.e. to prevent unauthorised people from entering the Temple (Tabernacle) precincts. If the word was meant to apply to the Kehatites, in what way were these different from all the other Israelites when it came to entering the Tabernacle? Furthermore, the next verse addresses itself specifically to the Levites which proves that the Torah did not address the Levites in the previous verse. The reason the Torah had to warn Moses was because we learned in Zevachim 102 that the priesthood was never taken away from Moses [after he had performed the sacrificial rites during the first seven days of the Tabernacle's inauguration. Ed.]. Even according to the view that Moses' appointment as a priest was limited to these seven days, I do not believe that he had been forbidden to enter the areas reserved for the priests. Our sages in the Sifri write as follows: "The words בית אביך refer to the Levites; this means that the Levites were instructed by the priests." I believe that this is an halachic exegesis, מדרש הלכה, an attempt to anchor the rules that have been handed down from Sinai in the text somehow.

2אתך, "with you." In view of the fact that the Torah already mentioned Aaron by name, why did the Torah have to write the word אתך? Perhaps the Torah wanted to indicate that Moses and Aaron had a joint responsibility in this regard at all times. We should not think that Moses and Aaron as well as his sons rotated the times of their responsibility in this regard. The word אתך defines that each party concerned bore round the clock reponsibility in ensuring that the sanctity of the Tabernacle be preserved at all times.