Sorry. Welcome to the world of the browser. The user is God of this world. Meaning, that you can't script an automated print. That would be "hijacking" control away from the user. The JavaScript "print" method sends a request to the browser. The browser responds by opening the Print Dialog for the user. The user can decide if/where/how they want to print.
Now, there is a rather convoluted work-around. I coded a system for a financial firm that did automated document/form processing. Users would browse to a PDF form, fill it out, and the server would process/validate the information, store in a database, and return the PDF to the user with corrected data. It would then automatically print, silently, to the default printer.
The key is to use a PDF. Embed a PDF JavaScript into the PDF. While the browser object model doesn't have a silent print method, the Acrobat/PDF object model DOES.
That only addresses part of your problem, in that it's still a document-at-a-time.
Perhaps a totally different approach. Provide a zip file with all documents, that the user can download to the desktop and do with what they choose.