Should I Say Something After Finding Out My 2 Cousins Being Freaky?

I recently found out something went down between my 2 “closest” cousins (21F & 23M in 2026) back in 2020. At the time of that event, I was already sensing something had already happened. My two cousins vibe was off, they were acting a little bit weird and “lovey-dovey”. Play fighting but wasn’t…normal, hand placements were oddly placed while the mood set between the two were definitely “connecting”. Always wanting to spend time together, basically inseparable.

Today, another family member (22F) had told me over text, 21F and 23M had done some freaky shit. It happened on a night where 22F and her sister witnessed 23M and 21F go into a room @1am, door closed and no noise. 30 minutes later, they both walked out, 21F came out looking ~satisfied~, cheesin, red, and hair all fucked up. Meanwhile 23M, was married, and walked out the room knowing what they just did, proceeded as if nothing happened. 22F and her sister looked at each other confused knowing what just went down.

Weeks pass, 22F and 21F are hanging out. 21F stressing finding a way to tell 22F what had happened that night. Nervously 21F coughed it up, 22F caught off guard and in disbelief. 21F claiming she had missed her period and saying she doesn’t know what to do. She then continues to talk about the situation and what would happen if the rest of the family had found out. 22F still shocked, stumbling on her words trying to say something. Another person walked in on the conversation and 21F startled, cuts the convo off and asks the person that walked in if they could do her a big favor, getting her a pregnancy test! Person then questions what she was needing it for since she was “young” at the time for those activities. Came back with the test, fortunately it came back negative.

Despite a negative result and other risks, 21F still continued to pursue more intimate relations.

Nothing continued afterwards to our knowledge…

What should the select few of us (4) that know do? Should we tell the family? Single ones out? Or die with this shit?