In my experience the answer is yes. In my fraternity there was a family that at one time had three of its four sons living in our house. They were unremarkable in appearance and manner but down below, they were astonishing.
I recall once when the membership was getting ready for a Saturday college football game. We had to be ready, in formal dress, to welcome alumni and family members by 9am. The middle son of the family was pushed out of his room and into the hall by his roommate. They were laughing and carrying on. The guy was grasping his towel as his roommate reached out and tore it form his grasp. There were about four of us in the hallway walking to the showers. All of us literally gasped. This guy's penis was probably about 10 inches long. It swung like a piece of garden hose. He never took showers at the house; he had a girlfriend with an apartment so none of us had known before that episode how large he was.
Of course, his younger brother, who was my age, was known to be a "shower" but no one had seen him erect. One day I had to get up very early for a flight and entered the shower. There he was, another 9 to 10 inch penis mostly erect but so large that it wouldn't get straight like a smaller man's penis would. I tried not to stare but it was pretty amazing. We all teased him that he'd marry the first girl who could take him all in. We were pretty close. He married his second true girlfriend.
As for the third son, he was the oldest and rarely around when I lived in the house. However, one of the older guys told me that he also tried to shower elsewhere because they had nicknamed him "mule" or something like that.
The fourth son came once for a visit, he was the youngest, and he was the least embarrassed about his physical qualities. Funny though, he wasn't anything like his older brothers. The other brothers were obviously large, even when soft. This brother was almost normal to my eye. That didn't keep him from bragging that his nickname was "the bear." I caught his brother's eye at the time and I could see that the brother thought he was full of it. Later that night, this drunken fourth son wiped it out for some girl's pleasure (she slapped him - she thought it was too crude) and a witness said it was merely average. Living up to the family tradition was hard. No pun intended.
So three out of four isn't bad for that family. The downside was that they felt they needed to hide themselves or be the subject of staring and pointing and people carrying on. On that issue I felt sorry for them, but most of us wanted to trade places with them.
Later the son my afe admitted that all of the brothers had "compared" and the youngest was larger than the average guy, but nothing at all like the other brothers. The joke around the house was that the mother must have had quite a time doing laundry, all that stretched out underwear; all that masturbating going on as they grew up. Of course we all suspected that the smiling lady in her son's pictures was probably enjoying the father pretty well.