Are there any online free psychology courses?

I know that MIT has a ton of their course materials online, I'd check there for starters. And no, I'm not going to search for you :P

Try here: https://www.edx.org/courses

I don't if it's exactly what you're looking for, but there are some psychology courses: https://www.edx.org/courses?search_query=psychology

These might help:

https://www.coursera.org/

https://www.khanacademy.org/search?page_search_query=psychology

http://alison.com/learn/psychology

TED talks are also pretty informative.

https://www.ted.com/talks?topics[]=psychology

If you want a video type only

I don't like politics, history and chemistry courses but I loved how they chunk their videos chronologically starting from the basics (history) to the more specific topics. Definitely recommending them

The psychology video playlist is complete and is around 40 videos

There's a Human Behavioral Biology by Stanford on YouTube. And you know how famous they are at this kind of stuff.

What exactly are you looking for for your story? Are you trying to make reasonable biographies that explan the character's current persona or the various personality disorders? Or just the basics? Psychology has a wide range of topics that are interesting. If you find a course that is good please hit me up, cause I want to extend my knowledge on that as well.
I've read Anxiety ISBN 978-3-497-02043-0 by Fritz Riemann. It gives you a really good insight on the impact of parenting (especially the wrong one) and how people work in general. I don't know how the english translation of this book is but if it's 1:1 you shouldn't care too much about the 4 types of people he describes or the titles especially because he uses terms of personality disorders that don't really apply to what he describes.It just helps the reader to remember the categories better imo.