We don't know the positioning of the individuals, for all we know OP and her dad could have been laying down and Mom walked up. As for the last question, some families have raised their children to be accepting of it. Hell, my dad had no shame and would grope my mom even if I was around. I paid no mind to it, because I'm comfortable with my parents and, whilst it's incredibly awkward to admit, parents don't stop having sex. I learned that through hearing them after muting my music one fateful night. Since then I just take their affections as is. They love each other. Better for them to laugh and play around rather than them screaming at each other throwing punches. Sure I may go 'ewww' at them but it's all in good fun. They know their limits haha. Perhaps OP is like that with her family. I'd rather have that than a broken, hateful home.