From what it sounds like, me and you have very similar situations when it comes to our stutters-I too seem to be able to speak almost fluently sometimes when around friends, professors, and coworkers but when I am with my family I suddenly lose a lot of the control which I have worked so hard for. I have always thought that my increased rate of disfluencies around my family is due to the fact I don't feel the need to necessarily hide my stutter in front of my parents. When I am talking to a stranger or a friend I try and hide my stutter as much as possible in an attempt to not be ostracized for it, but when I'm with my family I seem to be comfortable enough to not give a shit. So if anything I think you should look at this as a good thing; you stutter in front of your family because you feel comfortable enough around them that your brain stops caring