I've been best friends with him for 30+ years and have known his family that long also.
What would you all do? Tell him or keep quiet? And yes, she's hot... I know that will be one of the first questions...
Ask yourself what good will that do? You know him so you need to make that call. I would be more inclined to let her know what you saw. I would let her know you are not judging her at all just saying what you observed. I would make sure she knows that you are not hitting on her, after all she is your best friends daughter
As a father I would rather not know.
Have I found something similar? Yep, more than once and one was my niece. It was about a 5 minute video of her giving her husband (never saw his face but it sounds like him) a BJ including him cumming on her face. Per her request btw. No way would I tell my sibling I saw their daughter in such an act. Nothing to be gained.
I'd give her a shout and find out if it's even on the site with her consent firstly. Given she's an adult, I wouldn't tell him. That is her decision to make.
and spend less time on the websites hahahaha