I don't have any brothers and I only recall seeing my Dad's penis one time in my life. I know that a great deal of my size was caused by a pituitary tumor when I was young so I can't say if mine is hereditary or not. I have two sons, one is well above average and the younger is average. I have three grandsons, two of which were nicknamed "Meat" by the nurses when they were born. The weird thing about it is each of my sons have a son that was nicknamed "Meat" at birth. Maybe the mother's side does have some affect on penis size.