I just want to add here that, like most slang, you need to be careful when using these terms so as to avoid looking silly.
Personally I would call my group of friends "my group of friends". People do use terms like gang, squad and homies, but not often in my experience (I'm in my 30's so am probably a bit out touch though!)
My point is, if I called my close friends "the squad" or "my homies" I would be probably be laughed at. It's contextual, based on who you and your friends are, your culture and any pet names or in jokes you have. These terms aren't really just interchangeable or synonymous.