I am not close to my birth family, I left home as a minor and I rarely saw my relatives. Oddly we get on very well when we are together, discussing things, joking and laughing, but we make little effort to keep in touch. I have four brothers, I shared a room with my elder brother, he and I are circumcised, my three younger brothers are intact, my father is intact. My father was not inhibited about nudity with me and my brothers. We swam naked together. My brothers varied in their comfort with being nude with me, but I know what their penises look like normally, and during their teenage years what their erections look like.
My brothers, my father and I, do not look alike, you would be hard pressed to see a resemblance between us, but oddly enough as far as dick shape, size flaccid or erect given my younger brothers are intact, there is a definite family resemblance especially in shape of the shaft and volume, glans shape. Hair pattern not so much. As far as erect length, we would be in the 17 cm -19 cm range, and 15 cm girth.