@BetterRed: fundamental problem. Apparently you checked the "Contains Names" box for the tags-like columns, making the item separator an ampersand instead of a comma. This option does not exist for composite columns. Their separator is always a comma. Your template must take that into account.
Something like the following will give you a comma-separated list of authors in the composite column. To avoid unhappiness when resplitting the column later to make tag browser entries, I turn first all commas in names into semicolons. You would need to change the parameters to the field function to be your column lookup names.
Code:
program:
l1 = re(field('#people'), ',', ';');
l2 = re(field('authors'), ',', ';');
list_union(
re(l1, '&', ','),
re(l2, '&', ','),
','
)