BR gave you the
Plain Vanilla Calibre Way
Get (and install

) the Manage Series PI
Select books from Both (you can use the Tag Browser to select 2 or more groups)
Select All or Highlight all books: Launch the Manage Series PI
It will
try and arrange the order for the name at the top.
YOU ARE NOT required to use this name-just change it .
You can Reorder the books in the List
You can lock a book index thus creating a Gap
OR Add an empty book (place holder

) to fill gaps
This PI has Series POWER