Sex with siblings watching?

Has anyone had sex while a sibling was watching? Or even participated in the act? If yes, what was their reaction? To clarify: I do NOT mean sex with siblings or incest.

I was in my teens when with my brother and his girlfriend (both in their very early 20s) went skiing in the mountains. We rented a small bedroom with 2 beds, I took one and they took the other. In the early morning hours, funny noises woke me up and realized they were having a good time but kept pretending I was asleep, too scared to react. Next morning, a repeat session. Quite a few years later, with my then girlfriend we visited her sister and hubby. After a long discussion about relationships and sex and after a few more drinks, a sexy tape was playing (not sure how this started). Hazy memories, but I remember well we had sex on the couch, just straight sex, each one with their partner like couples, never swapped partners. I remember there were times the sisters were holding hands. Next morning, I woke up with the guy's genitals just inches from my face. Again, no recollection of what transpired. We were all naked and with a mild hangover. We spent most of the morning naked and just being lazy. Unfortunately, never repeated the experience.

Technically no, but here’s what happened. In February of a few years ago, my family came to visit, including my twin sister. Me and my wife that night had (apparently) some really hard sex, as my father complained that it was extremely noisy last night. My sister asked me what I was doing and I told them the truth. They didn’t seem to care much.

My mother said she didn’t hear anything, I think she needs to get her ears checked maybe.