What mental disorders come from sibling separation?

You would have to do some searching for journal articles about case studies for answers to this. Is this for an assignment? If so, I suggest you go to your school or college library and ask the reference librarian for help in searching the right databases. Or you could search a public library’s social science and general scholarly databases for relevant articles. Hope this helps.

There is a fruit basket full of possibilities.
Consulting a professional is the only way to get a true scope.

Separation anxiety.
Watch the documentary Three Identical Strangers. Really good.