Brđanin has the right to declare himself Srbin from Crna Gora, the others will state their ethnicity for themselves. It seems to me that Brđanin is trying to act as the Greek reporter on the above video.

I do not see it as my "right". it is more of an obligation toward my ancestors and their legacy.
their names are on the hero monuments of Balkan, WWI and WWII wars.

Hardly… You have close slavic people which are not devided with religion, and nothing happend. Slovakia-Czechia, Russia-Belarussia-Ukraina, and in the end you have Serbia and Montenegro. All of this countries have strong national identity which is rooted back in the, not ancient, but that old history.

maybe, maybe not. but Croats, Serbs and Bosniaks still share the same language. IMO language is most important thing when it comes to ethnicity. But of course that is just hypothetical thing.