MBKMS explains such a heart touching story...
Mike: He is who we get control on, the main character of this storyline. He is good in all the fields but not upto his brother.
John: He is Mike's brother, elder brother. Always ahead of Mike in whatsoever and always insults Mike.
Mr.White: He is the father of the two brothers(Mike and John). He treats both equally but maybe treats John better than Mike. Although we don't see him much in the story he plays an important role in getting a start to the real story.
Ashley: He is Mike's best friend. He is our partner for a very long duration of missions. Unlike in MBKMS non-improved he plays a good supporting role in H I.
Melvin: He is the one sent to kill Mike by John. He accepted it for his own good too. He shows us his good side first which slowly turns bad.
Sean: He is Melvin's younger brother. We actually see him in just one mission, but the story is not possible without him.
Catherine: She is Melvin's younger sister who came in to distract us. Without revealing her identity she slowly tried to do the same job as her brother.
Charlie, George and Peter: They just wanted us for their need to rob the biggest company in Las venturas.