I've read about Hasan Predojevic and Stanko (Skanderbeg) Crnojevic alot. Bosniaks claim them as theirs. How can this be? Predojevic is a noble serb house from Hercegovina whilst Crnojevic is a serb high nobility.

http://en.wikipedia.org/wiki/Hasan_Predojević – Hasan Predojevic serb convertite.

http://sr.wikipedia.org/wiki/Станко_Црнојевић – Skanderbeg Crnojevic also a convertite.

Is the religion the main factor or what is it then? Many bosniaks seem to see the islamic faith as the sole bosniak thing. And of course the Stecci stones that aren't slavic at all but Vlach/balkanian (illyr/thracian) in origin.

Most of Sanjaklije are former Serbs who converted to prevent biological turcification which was conducted on their fellow Serbs, primaraly nobility etc. While New Serb nobility .ie anything starting or ending in Kara are the previliged bastards of Turkish lords which governed the Serbia region.

While the same can be said of Bosnian Serbs who are composed of Serbs proper from Old Serbia (settlers brought to fill up the holes left by plagues and aftermath of Hamzi heresy), Romanian Vlachs and Catholics who were forced to convert after Krajina fell to Ottomans.