All are correct, just two things “He had never been IN Kyiv before he started to study in this city”.
And the 4. If you are talking about your brother in the beginning, it would be better to say it “After my brother had finished school, he became a student.”. The past perfect describes the action done in far past, therefore you don’t go from the far past to present, so “becomes” gets replaced by “became” .
I hope it helps, :)