1)
What are the connotations of ?ve?Itchem Yih?hu ? ??
1.
Rashi: It means that, when Moshe and Aharon counted the tribes, the Nasi of each tribe stood with with his tribe whilst i was being counted.
2)
Why did each Nasi need to stand with Moshe and Aharon when they counted his tribe?
1.
Seforno: Because he knew the members of his tribe and was able to corroborate their lineage.