In the South we count all relatives. The ones we like and the ones we don't. Some we hide but when asked we'll admit it. Weirdness is a relative statement, if you doubt me, I'll introduce you to some of my relatives. I grew up with lots of cousins and second cousins that I merely called cousin. I have one second cousin (whose son, a third cousin I just called cousin) who I still call Aunt even though her brothers I have always called by their first name because they were cousins.
In addition to counting third cousins, in the South we use removed. Second cousin once removed, etc. I had a Great Uncle I just called Uncle, his daughter I called Aunt, but his Grandson (a second cousin once removed) I just called cousin. Speaking of, has anyone heard from Keith lately?
If you need to understand half and step siblings, ask a Southerner. You're more likely to get an understandable answer. We also get, laugh at, and maybe even know someone who is like the Ray Stevens song, I'm My Own Grandpa.
With all this attention to relationship detail it makes me really wonder: why is there no accurate way to distinguish between in-laws? I can't tell my sister's husband from my wife's brother because they are both merely brother-in-law. Maybe that's where the kith comes in?
A completely unrelated grammatical question is, why is the plural of all in-laws different from the plural of one type of in-law (i.e. in-laws versus mothers-in-law)? ~~~~~~~~~~~