genetics maybe !!
I WOULD SAY THEIR UPBRINGING IMPACED THE COURSE OF THEIR LIVES.
Are you are females?
It could be as much to do with the way you live, schooling too, as your parents. If you have friends and interests they're not a severe depression going on. And, in life as adults we make ourself happy, or not
I'm a psychologist, so if someone has friends and interests this suggests the depression isn't severe. Maybe you want to be a victim and blame your parents. Be my guest
Or you could have clinical depression which is genetic and not environmental. At least as far as I know anyway.
I honestly don't know the details of the genetics but it's not remarkable for all siblings to have the same hair color.