A book you can read about Escobar is where his own son Sebastian Moroccan wrote it. Pablo Escobar
Now for Felix Gallardo the truth is that I have not found anything relevant, maybe another person who may have read something can tell you. However, I have read the following book Narcoland which is written by Anabel Hernandez, Mexican Journalist and Author, and it's the best I've read!.
Eh i'm not so sure. His son wrote a book if you are interested but I also think he downplays some aspects. In an interview he scoffed at the idea that his father was worth billions at one point. So Im not really sure how credible he is. Pablo Escobar: My Father - https://www.amazon.com/Pablo-Escobar-My-Father-Juan/dp/1250104629
Pablos Brother has also written a couple of books.
https://www.amazon.com/Escobar-Roberto/dp/0340951109
https://www.amazon.com/Accountants-Story-Inside-Violent-Medell%C3%ADn/dp/B005DI8F24