Why does the Torah here write "Aharon u'Vanav" (in the plural) amd in the following Pasuk, "be'Yad Isamar"?
Rashi: Pasuk 28 explains Pasuk 27, as if to say 'which of the sons? Isamar'. 1
Ramban: The current Pasuk refers to Aharon and his sons, who appointed every ben Gershon 2 to his specific task, 3 including whether he would sing or whether he would stand guard. Also when they traveled, they did not dismantle or load on to the wagons, until they received the go-ahead from Aharon and his sons. 4
See also Sifsei Chachamim, and the Ramban, who queries this explanation.
However, when they returned the Keilim after traveling, each one handed it to Isamar who was the officer in charge of Gershon and Merari, and declared 'Here are the Keilim that were placed in my charge!'