Do I have to include full gpl v2 license information in my commercial project if I use another author's work?

Question

I would like to use another author's work in my commercial project.

That author's work is licensed under GPL v2.

I'm not using full code. I'm using only part of the code. Also I modified it as per my project needs.

Now i'm confused about what kind of license information I should include.

This is the full license text.

I'm using multiple author's work in functions.php file. Some works are licensed under MIT.

1) Do I have to include full license text in my php file as a comment?

2) Do I have to create separate php file for each author's work.?

Answer 1

Do I have to include full license text in my php file as a comment?

What you need to do is spelled out in the "How to apply these terms to your programs" text of the license text you linked. It says:

If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.

To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the "copyright" line and a pointer to where the full notice is found.

<one line to give the program's name and a brief idea of what it does.>
Copyright (C) <year>  <name of author>

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

Also add information on how to contact you by electronic and paper mail.

Do I have to create separate php file for each author's work?

The GPL doesn't require this.