I believe that all the NG troops fall under the command of the NG to whose mission they have been tasked. In this case, that would be the Commanding General of the DC NG, who reports to the President, (or currently FEMA, given the Emergency Declaration). It’s inconceivable that the NG contingents from around the nation would not be subject to a single command structure.
If TW is correct in his recent predictions, many will be happy