I've been stammering for the last 25 years now, even though I don't take speech therapy now, I did for 4 years and to be honest, it haven't helped me a lot. What you said is true in my case, I stammer a LOT more when I'm around my parents, specially while talking to my dad. I'm closer to my mom than my dad, maybe that's why I don't stammer as much when I'm around her. Recently the stammering had got worse and that's what got me thinking about it so much and noticed that even talking on the phone with my parents increases my stammering a lot. I do ok-ish when I'm around my friends whome I'm really close with. On a side note, I'm from the Maldives and my native tongue is Dhivehi. I've also noticed that I stammer more when I speak in English. But it's also an advantage to me because I can sense the words that I'm about to a stammer at and it gives me a chance to change that word to an English word when I'm about to stutter. In my opinion, I really think that stammering more when we're around our parents is because we tend to show our best to them. We don't want them worrying about us much and that's making us think more when we speak to keep our speech perfect for them.