@Aroused Your experience with your grandmother and her 'generous' friend passing on clothes for you to wear certainly made me wonder how many boys she got to see in the nude if all the mothers and grandmothers took the same attitude to modesty as your grandmother, she must have gained quite a wide knowledge of boys development !
My mother did a similar thing with me once when I was 16 and not long out of hospital after an operation which left a scar from upper stomach down to my shaved pubic area. When her two friends visited, as my mother was still nursing me and couldn't go out, they asked how I was feeling and did the scar, which they could see above my pajama trousers, still hurt.
As I was explaining that it didn't anymore my mother told them that it went right down across my stomach then to my horror undid the pajama trousers and let them fall to my ankles whilst saying 'John won't mind showing you'. Having no top on, it was very hot that summer, I was then naked from the ankles up with her two friends inches away from my genitals.
Nobody touched me, unlike in your experience, and to be honest her friends looked as nearly embarrassed as I was but stood there for several minutes almost completely naked (ankles covered!) and to make it almost worse shaved from thigh to chest it seemed like an age before my mother bent down and pulled up my pajama trousers again.
As they were mothers two best friends I continued to see them about and in church and I always felt awkward when one of them was with her daughter, wondering if it had been discussed in front of her at table that night.
I spoke about to my mother years later but she only said 'Oh you were only young I didn't think you you would be embarrassed' I reminded her I was 16 at the time.
I doubt a daughter would be subjected to that in front of male friends - double standards I think.