Hm, you might be surprised
Croats and Serbs are biggest enemies when they are "facing each other", but they mostly co-operate against rest of the world, and especially ex-Yugoslavia
When we are talking about idiots of course then:
Slovenians are "selfish and self-centered, they don't belong here anyway", Macedonians are "okay I guess, they are nice people, but they are so irelevant, who cares about them", Bosnians are "stupid" and also "they don't exist actually, they are just Croats and Serbs converted to Islam", Hungarians "don't have sea and that's great because they were occupying us for centuries", and Albanians...ah, Albanians...better not to start about them....
So, I wouldn't be surprised to see Serbo-Croatian lobby actually
BUT, very important thing is what are they by ethnicity. For "Croats" I can say that girl is certainly Croatian, while guy is Moslem, I would say by his name. Slovenian guy is defintely Macedonian by ethnicity, so all of that can be important when they will decide who will audience vote for first time.
To be honest, I would be surprised if first nominees wouldn't be Albanian girl and one Slovenian.