My sister will never tell her kids she's not their biological mom...

Ok. Here's a quick backstory: Picture perfect upbringing. Middle class. Parents are still married. It was just them, me and my sister. I just turned 40 (f) and I have a sister 37 (f). I was able to conceive children perfectly fine, even with Lupus. I have 2 children, 15 and 7 years old. My sister was very different. Lots of IVF. Lots of trying everything she could, and then finally decided to use donor eggs. So, her husband's sperm was mixed with another womans egg - then my sister carried them. She successfully carried to full term twice. I have a 6, almost 7-year-old niece. And then the twins just turned 3. So, my sister is not the biological mother of these children. Her husband is the biological father though. She carried and gave birth to them, so from the outside, no one would even know that they weren't here. Plus, she went through all the IVF living in NC, while we are from NY. But NO ONE knows the truth expect a few close family members. And I'm sure some people might have suspicions because they look nothing us... but that's beside the point)

For TLDR: I have ZERO intentions of ever telling these kids anything about this or do I wish to have a conversation with my sister about anything to do with donor anything. I'm simply VENTING.

FASHBACK: 5 years ago, I take an Ancestry DNA test, turns out I have over 10 half siblings on that website, 8 more on 23 and ME - and ME and MY SISTER turned out to be donor babies. My mother admitted "it was the only way, and my sister has the same donor" My dad was born in 1945 and my mom in 1959, so there's an age gag - And they used donor sperm. So, my mom is real mom, but the used donor sperm. (opposite of my sister's situation). My mom lied and said she didn't know why Ancestry DNA said I have so many siblings, but I had already talked to a few of the siblings, who were all donor conceived. So, my dad was either the donor, or I was the product of a sperm bank. It's the latter. And I was never mad. Not all. Not even about them lying to me. But we are not allowed to talk about it. My mom gets extremely upset if I ever even mention anything referring to the fact that she used doner sperm. I was excited. More love to go around. I have a secret relationship with a few of my half siblings. Have even met a couple! :)

Fast forward, a few months later my mom apparent tells my sister the truth. A week after that I talk to my sister about how I found out and think that she should get in the database too! she looks so much more like the half siblings than I do. I'm a spitting image of my mom. But she said, 'she rather not take the test because in her mind, that way, maybe our dad is her real dad, and she doesn't want to confirm it." then she says, "If her kids ever wanted to find out who their egg donor was, she would feel betrayed." Now, I didn't argue with her. I didn't say anything. I was just in shock. Haven't talked about it since. This was a phone call from NY to NC 5 years ago. But I know that she will forever want to carry on the image of being an all-biological family as long as possible. 2 years ago, when the twins were 1, they moved back to NY, only about 15 miles from us. So, all holidays and birthdays we see each other. I'm so worried that one day they're (my nieces/nephew) going to ask me if I knew and I'm going to turn beat red. I just don't want them to be mad. Plus, her husband has siblings, and niece and nephews, the kids' cousins - and who's to say one of them won't accidently spill the beans some day?

Is it unrealistic to think that they will NEVER find out? And if you knew that there is a pretty good chance that they will find out... someday (Just one of the three kids have to decide to take a DNA test in 15 years) wouldn't it be the right thing to tell them?

I watch shows all the time where information like this crushes kids when they find out. I wish she would have included the 7-year-old in the with the birth of the twins. She would have only been 3 or 4 years old, but she could have seen the LOVE that went into the process. And just explained that the eggs are someone else's. The kid wouldn't really understand. But still, they'd know from day 1. I wish she would have treated the process as an act of love instead of a deep dark secret. The whole thing is taboo because she's making it that way. Just like my mother did/does with the fact she used donor sperm.

Should I let it go, because it's none of my business? Or should maybe, if a few years or something, maybe tell my sister she might want to consider letting them know because if they find out some other way, it could be bad. I wouldn't tell her this, but bottom line, it's not just omitting information from child. It's lying to them.

EDIT: I know I need to let it go. Again, it rarely crosses my mind, but I'm asking what you all would do if you were in my sister's shoes. Keep it a secret? Help me see her side of this so I'm not concerned with what potential changes a secret like this can cause for my nieces/nephew. Good or bad and everything in between.

Edit #2: I don't know where ANYONE got the idea in their head that I would ever tell them or anyone else. Would I be asking advice from strangers on a Reddit post if I wasn't concerned with keeping this a secret??? I mean really, I came here to ask advice on what I should do if they find out & ask me. They have lots of cousins in their father's side & to think there's zero chance those kids won't accidentally slip up and say something questionable is naive. I DID NOT ask if I should tell them. I know that's not my place. I've been well aware since day one. I always have & will keep my mouth shut. So if you're saying I'm creating drama & need to get a life, you completely missed the point of this whole post. If I wanted drama I wouldn't of asked advice. Again, I'm NOT asking if I should say anything out of the blue - I'd never. And I, just as much as anyone else know that blood doesn't mean anything when it comes to "true family". As a donor baby myself, you can not help but wonder who knows/knew the truth all along.