Sometimes. But often, if you have what in this case would be (supposedly) multiple suspects on a specific crime, you would empanel a special, separate grand jury because a sitting grand jury is going to be looking at “ordinary” crimes.
This will be a complete and utter whitewash. Let’s face it, Barr is still having the Mueller’s over for dinner while their wives go to church together. Barr knew from day one, Mueller was an incompetent bumbling fool who was not running the Special Council.