As for the topic whether Shtokavian, Kajkavian and Chakavian were related to particular tribes:
A dialect means for sure an earlier common contact of the speakers in question. But as for the lingusitic "ancestry" of these dialects I've hat a look for the "what?"-word in other languages. Interesting is that you do have both "shto" and "kakov" (the latter is obviously related to the Kajkavian and the Chakavian "what?"-word) in Russian, see pic:
https://i.imgur.com/sbEfG9X.jpg
To me this indicates that it's not about real language differences, but just more about what word usage has developed to be common, the shto or the kak word. Such a thing might have developed comparably late and must NOT be linked to from where the Slavic settlers of a particular later spoken dialect initially came from. (Other traits of the dialects may give hints for origins, but I think, that the "waht?"-word does not.)