I too stutter the most around my father, or I did anyways, nowadays It's is alright when I talk to him. But it's still there when I get stressed or nervous and try to say something to him. It's weird. Stuttering is so psychological! It's all in your head, haha. For me strangers + important situation + nervous/stressed out = mutism. I had the privilege of experience that equation today actually. I probably said ten "um's" before she interrupted me and began guessing what I wanted to say.