Auto-import and export for author

Hi 🙂

i have a question…i have different authors in my blog.
i’d like them load (every night..) their content from their WP site…they export their XML file and i’ve to import them.

but i have few questions :
– post already loaded are duplicated?
– can i make the procedure automatic? can they upload i file in a folder (via ftp? or store them somewhere) and then the import function retrive them all?
– author doesn’t have the “tools -> import/export”…how can i grant them the right to export (cause i don’t want everyday or when they need this to login, export ect…..).
of course i can’t make them editor or admin…

thanks