This is so difficult.
I have namechanged as family circs might make me easy to identify.
My grandmother had a child in the 1920s before she married my grandfather. Child was adopted by a family in her village. When my GM was 90 she decided to trace child, now 70. Used private detectives who waived fee owing to age of all concerned. My parent and siblings met half sibling, said hi but AFAIK have not really maintained contact.
That's one side: BM traces child.
Now, my DH and DSIL are both adopted.
DH's BM made it clear in adoption notes she was up for him getting in touch when older. He did and they had a good relationship (they were kindred spirits and filled the gap he had always felt at being nothing like his adoptive parents, lovely as they are) from his early 20s until she died about 10yrs ago. She gave him his BDad's details - he got in touch and his BD wrote back to acknowledge but to say he couldn't really strike up a relationship owing to new family situation. Think DH thought this was a bit weak but respected it (BD had disappeared by the time BM found out she was pg but she had written and told him. She had DH at one of those bad girls' homes, though I don't think they were quite as bad in the UK as the Irish ones.)
So there we have BM giving out BD info, although in this instance BM was the 'good guy' and BD the 'bad guy'.
DSIL didn't have the open door to BM that DH did, though of course she knew who she was. She had a friend track down BM and get in touch in her behalf but BM just wasn't interested. No info on BD but I guess she can't help wondering if BD would have been the 'good guy' to BM's 'bad guy'.
JJ17 I sympathise with your not wanting a hnd-grenade thrown into your family dynamic. But no matter how happy one's adoptive situation, adopted children (and don't even get me started on the adoptive parents who don't tell their children the truth) wonder about their origins. I'm not adopted but there were times (particularly as a teenager) when I thought 'Who are these parents? They are nothing like me!'. The difference is that as you get older you can see that actually they are like you (or vice versa) after all. Adopted children may never feel that connection, no matter how much they love their adoptive parents.
Sorry for the essay.