No, Miracast itself does not support broadcasting. To project your laptop screen to multiple ViewBoards simultaneously, please use the AirSync "Group" feature or ViewSonic Manager.
Solutions:
AirSync Grouping:
Launch AirSync on the primary ViewBoard.
Use the "Group Connect" mode to include other ViewBoards on the same local network.
Content projected to the primary display will be broadcast to all grouped screens.
ViewSonic Manager:
Note: