as Tinkeringbell noted in the comments you definitely should reach for help at the institutions you already were in contact with, this is surely not the first case like this
I am not personally anywhere close to a situation like this [ in[in response to your comment ]comment]
This answer might seem harsh and inconsiderate but I am trying to balance between what you are lawfully allowed to know, what you would like to know and what might be the interests of your siblings
I would adviceadvise you on viewing siblings more as a sort of 'forced friend', in the sense that you are basically forced to grow up with them and interact with them. Also they are often in the same age group, which makes a kind of 'friendship' easy, although this does not always have to be the case, just as not all friendships last forever.
The only difference to a 'normal friend' is that you also share a lot of things just by being in the same household. Same authority figures, same house, eating together, same festivities, common familiyfamily activities, ..etc.
In your case you share very little. In fact the only thing is that half of your gene pool comecomes from the same creature - your mother. And that is almost meaningless. In fact there is almost no difference in the relationship between you and me, and you and them.
They are total strangers who might have some information you would like to have and thatsthat's how I would treat them. At least kind enough to get the information, more if you feel like it.
I think the situation depends on why your mother gave you away. She could have done it for a good reason (i.e. to prevent poverty, disease, death, ...) or she could have just regretted being pregnant with you and tried to get rid of you in order to not have to confront her mistakes.
So I will guess that it is a minor issue, in which case I tend to recommend you try to arangearrange a meeting via the agency of the institution.
Before the meeting/Whatwhat you should be mindful of
remember that these people have not much more in common with you than I do, and you wouldn't assume that we two are going to form a friendship now, so don't expect it from them either
they are likely very different from what you imagine, so keep your expectations low
they are total strangers, so don't trust them more than any other stranger just because you think they are related to you
be aware of what you really want from them and what you are ready to give to them (concerning: relationship, information, maybe even money issues, they might care about inheritance of wealth, ..etc.)
The biggest danger I see is them trying to manipulate you. Especially when there is a noticeable difference in wealth or social status. That's why I recommend to thinkthinking a lot about what they could bring up. Are there touchy topics in the letter from your mom? What if there was a recent family death? Who is your dad? Are you entitled to inherit anything if your mom were to die? Should you contribute to a funeral? There is so much but I think the best thing to keep reminding yourself of b during the conversation is:
You didn't do anything wrong, you are not responsible for their potentially fucked up family situation, you were not the one to cut contact, you dont don't have to pay any compensation. Nothing.