Firstly, Kobo do not use a separate "author" and "author_sort" like calibre. They only read what is in the "author" field and then try and parse it as a name.
Yes, Kobo uses the comma as a separator for multiple names. But, it should be sorting on the last name of the first author.
Code:
Ln1, Fn1
Fn1 Ln1
Fn1 Ln1 and Fn2 Ln2
Fn1 Ln1, Fn2 Ln2
Fn2 Ln2
Fn2 Ln2, Fn3 Ln3
Fn2 Ln2 & Fn3 Ln3
Fn4 Ln4
In the book list, it will use an ampersand or the word "and" as the separator. I'm pretty sure that's how that list would be sorted, though the ones with the "and" and "&" might be one place out. That means that "LN, FN" works, but, it is treating "LN" and "FN" as separate authors. And "Ln2, Fn2 & Ln3, Fn3" will probably sort correctly as well.
In the Authors list, only the comma is used as a separator. From the above authors we would have:
Code:
Fn1
Ln1
Fn1 Ln1
Fn1 Ln1 and Fn2 Ln2
Fn2 Ln2
Fn2 Ln2 & Fn3 Ln3
Fn3 Ln3
Fn4 Ln4
I think that is the right order when sorting the authors list by lastname. But, the ones with "and" and "&" might be one place to high.
A problem names like "Fn von Ln". This will treated as lastname "Ln" with first names "Fn von".
Because of this, the authors part of the metadata plugboard I have been using for a while is:
Code:
program: raw_list('authors', ', ')
If you want to do anything else, you will need to replace the spaces and possible the comma with some other character. I remember a discussion here a while ago where someone did this. He wanted a "Fn Ln" to sort using "Fn". Replacing the space with an underscore would work, but he might have found a less visible character.