Is this the same command to take 12 men as above (3:12)?
Malbim: No. Refer to 4:2:2:1.
Above (3:12), Hashem commanded to take "Ish Echad la'Shevet." Why did He command here "Ish Echad mi'Shavet"?
Malbim: Above, each man is in place of his Shevet [to witness the miracle]; he must be the Nasi. Here, they need not be Nesi'im.