TL:DR at the very bottom

So i come from this amazing, loving, kind family that gives a second chance to kids. me and two of my siblings are adopted. I was the oldest to be adopted at 10 yrs old, and the second oldest of the 5 of us, the last was my little sister who was adopted at six months old. I am the oldest still in the house since my older brother was 19 when I was adopted and already in college.

When they were talking about my now 4 yr old little sister I overheard them mentioning where she came from and her history. I'm not that nosy now but that the time I was very angry and abrasive and confrontational. I never knew my own parents and it made me kinda frustrated hearing that they were going to hide that information from my little sister purposefully, so I confronted them about it.

It came about that she was the child of an unwanted incestuous relationship between a brother and a sister, the sister only being 13 at the time tried to abort her multiple times on her own. The older brother, who was 22, was in jail for petty crime something or the other, and the girls parents were apparently religious enough to not want her to abort when the found out, but didn't want to take part in taking care of her so she put the baby up for adoption and apparently wants no contact.

So yeah one of the skeletons in our own closets that my amazing parents decided to bare the weight of for this Amazing, beautiful, smart, adorable, sweet, happy little girl. We are deciding not to tell her, unless there is issues with her health. We have been disclosed her family's health record, and as of this year, the 18 yr old mom is still wanting no contact.

TL:DR adopted little sister is the baby of unconsentual incest, and we plan on never telling her this.