They cannot pull them onto the VTT, because the assets are not in their libraries. If you want them to assemble villages and similar, you will need to place the assets onto the tabletop yourself. Once they are on the board, your assistants can manipulate them. I'm pretty sure they can even copy and paste, but I can't guarantee it; I've never tried. Finally, if you want them to be able to manipulate the graphics, but don't want to manually assign user permissions to everything, you will need to give them GM privileges within that game.
