Getting Rid of Comma before 'and' in Authors' Names

The comma in front of the word "and" is a so-called Oxford comma. It is correct English but not mandatory. You may read further information here on english.stackexchange.

As it seems to be a matter of localization (more used in the US than in the UK), a possible "fix" should be provided by the chosen bib-style or the general localization done by babel or alike. It is not necessary to hack that issue yourself.