I (20M) also stutter a lot more with my family, I can only explain it like this: with strangers I have the opportunity to present myself as someone who does not stutter, it is a foolish intention since I cannot hide it even if I wanted to. But at least for a while I feel like someone doesn't know I stutter (and that makes me feel better). Around my family, I feel the pressure of them knowing I stutter (as them expecting me to stutter), so that's what I do. So the expectation has a huge impact on my stutter. If someone is expecting me to talk or stutter, I am sure gonna do it :) . If I talk whenever I want and not when I'm supposed to, I usually don't. Idk if this makes sense, but it's how I feel it.