So my understanding is that you can use "hangi" if the houses are not able to be referred to as the first, second, third, etc house. Can this sentence be used interchangeably, structurally speaking? "Fil hangi evde"?
yes, if you are not asking for the number. for "hangi" you would expect an answer like this house, that house, the rad house etc
does (kaçıncı) means which??
Kaçıncı means: "ordindal which". One could say: the "howmanieth".