@PaperDoIIs The possibility of having (had) an accidental relationship with a sibling could be a very real issue, couldn't it. I mean, how would you know?
I was brought up in a (then, by the standards of the day) rather abnormal setting; by the parents of my father - and never saw my mother when I was a child (met at 16). What I did not know, and was never told - was that they, in the death throes if their relationship, had had another child (as well as my sister while they were still together - and she stayed with my mother, and I didn't know her either). This was a boy, and he was adopted, after spending weeks in hospital/an incubator.
Many years later, he had a near-fatal accident, and decided to track down his birth "family". The official people went to my father's mother for some reason, and she delegated the task of meeting him, to me. I was agreeable, even though I had never been told of his existence. I was at that time, a few months pregnant and semi-happily married.
When we did meet, we had an instant connection - that, had we not know that we were biologically related, could have developed into another type of relationship. Thank God we never met without knowing the backstory, as much as we did. I get chills when I think of how it could have played out.
And for a while, he was slightly inappropriate; even though he had the most lovely girlfriends, he would tell me that he wanted "one like me". But I do think that it was the blood relationship underneath everything that was the real connection - and even that only lasted for a while.
So I aided in meeting his/my mother and the other members of that side of the family. I think it went OK, but I was not really further involved, as my mother then decided to shut me out (ho hum).
His main wish was I think to meet our father, who then lived in the south of France. They spoke on the phone, and he said that my brother was free to "call in if passing". (!!) Twelve years later, they did meet. One time only.
As recently as three years ago, my father inferred to me that - despite blatant resemblance - he would want a DNA test before meeting him again. Fortunately for him, my brother has no real wish to see him again - and he is even further away now.
The family who adopted him treated him very badly as well, so it has been a nightmare all round.