As an adopted person "biological <insert title>" has worked well for the parents that had sex to make me. For a donor parent, I probably just use "donor <insert title>". I'd advise not worrying too much about the language though. Being kind and thoughtful is far more important than selecting the correct words. A snap judgment selection of proximal words is sloppy but it's impractical to pause to select exactly the right language in all cases for all statements. So too with something this sensitive it might be good to slow a little.

My main point in the last comment is that inserting himself into their lives at all is disrespectful. He doesn't need a word for them because he has no relationship to them: he was an anonymous donor to enable their actual parents to have kids that they wouldn't have otherwise been able to have.

>inserting himself into their lives at all is disrespectful.

Keep in mind that he's inserting himself into their lives to give them millions of dollars.

Between these two choices:

1) Durov doesn't say anything, insert himself anywhere, or call you anything.

2) Durov gives you millions of dollars, but calls you his child.

I bet my life savings that every single kid will be fine with being called Durov's child in exchange for millions of dollars.

Exactly, even #2 requires child consent with proactive step to prove paternity via DNA test. There's also a third option:

3) Child chooses to ignore inheritance.

What child is going to choose to ignore millions of dollars? But true, that is an option I suppose.

Agreed, it's highly unlikely. But they have a choice, it's not forced by anyone. If they do nothing (maybe their parents never tell them, or they don't read news, or facial recognition never informs them of similarity), there's no inheritance. If they take consensual action to make a claim via DNA paternity test, the inheritance can be claimed.