Try this:
1) Unhide them. You could also give them target arcs containing the Shermans, or give them direct target commands although direct targeting seems to make them more likely to fire their small arms, so just unhide them with a target arc.
2) Give 3 or so pause commands to give them enough time to fire the Sherks.
3) Plot a Quick or Fast move order. If you want them to stay in the same place you can plot the move order onto the same spot they are already at.
4) Highlight the move order cube thing by clicking on it. You can now issue a hide command that they will execute after the move is completed. You could also give them a short covered arc on the end of the move to ensure they don't jump back up and start shooting again.