It’s so variable (the number of Type 1s in a family). My family is full of Type 1s (and some Type 2s). My youngest brother, myself, my grandmother, and my great-grandmother were all T1 (all as adults except my great-grandmother).
For your other question (about non-diabetics “stacking” carbs), yes they go up more or less just like a diabetic. However, their “normal” insulin response means that they don’t usually spike as high, or stay high as long, as either a T1 or T2 diabetic. A T1 diabetic with no endogneous or exogenous insulin has no way to bring a BG down, and so they don’t come down at all (other than the very inefficient kidneys excreting glucose through the urine after filtering blood). Most T2s in the earlier stages will spike higher than a normal person, and will stay higher than a normal person for longer (due to insulin resistance), but will produce enough insulin that they’ll usually come back down to “normal” ranges at some point. But, many Type 2s lose the ability to produce enough (or any) insulin after years of having the disease, and they become insulin-dependent (and have similar issues to T1).
But normal people definitely spike when eating high-carb meals, but they usually come down to “normal” ranges within two hours.