Voices are definitely hereditary. My father and his two brothers sounded absolutely identical. Of their children I am the only one who has inherited the distinct Gladnick voice. I first realized this when I was 16 on the phone with an uncle from my mothers side and he shocked that I sounded exactly like my father. Before that I had the basic kid’s voice.
My wife and sister sound identical. On the telephone I could not tell the difference. I had to be careful as they would sometimes play tricks on me.