Here it says "v'Samchu Aharon u'Vanav". Regarding the bull and the second ram, it says "v'Samach Aharon u'Vanav"!
Da'as Zekenim: Perhaps here they all did Semichah together 1 , and for the others, first Aharon did Semichah, and afterwards his sons. Perhaps "Aharon" is written full, with a Vav 2 , to add the Vav to 'v'Samach' of the others, to read v'Samchu, i.e. for all, all did Semichah together.
Semichah must be with all ones's strength. How could five men fit their hands on a ram's head to lean with all their strength? Menachos 94a says (for Tenufah) that if one's hands are on another's hands, this is a Chatzitzah! (Perhaps the Yerushalmi argues - Tosfos Menachos 61b DH Kohen.) And how could the ram's head bear all that pressure? Perhaps it was a miracle (PF).
Minchas Shai: In accurate manuscripts and old printings, there is no Vav. (Our Seforim do not have a Vav - PF.)