<<< I want to share a printer but they say it can't, even though it has a printer&faxes folder installed on the drive. >>>
A USB/Parallel printer is shared in a network in one of two ways:
(a) Most commonly, by connecting it to one of the networked PCs and setting it as "shared". It is then available to other computers in the network provided the 'host' computer is running.
(b) By installing a "Network Print Server". This connects directly to the router by ethernet cable or wirelessly and has the necessary printer port (USB or Parallel) with which to connect the printer.
There are also printers with an ethernet interface, designed to connect directly to a network.
<<< I only seem to be able to get it to share a folder with everyone or not at all. >>>
You may need some third-party encryption software or similar to control which computers access which folders. A NAS drive's "raison d'être" is normally to host files that are to be available to all computers in the network.