??? If your Libraries are by Author, why would you need a VL?
The Tag browser can do that filter.
You can combine Calibre Libraries
fairly 
Easily
In all cases The Target will be 'Mainlib' (or the name you chose). It must exist
Simply
View the source Library: Select all Books (ctrl-A): right click: Copy to Library: Delete (entry)after copy: Mainlib
Repeat for each source Library
You can later remove all the empty libraries using the OS (there will be no Author folders if Calibre thinks it has done them all)