You have no idea of the vast depths of your ignorance which you have just betrayed.
> But I do understand the Abernethy's were at one time considered royalty
The Scottish Abernethy family were never higher in feudal rank than a Baron. Which does out-rank a Knight but never came anywhere near the heights you envision.
You are, however, correct that last title holder of the Abernethy family never had a male child. Or female, for that matter: the 9th Baron never married. After his death the title was in abeyance for a time until it was bestowed upon a member of the Fraser family, where it resides today. The Scottish Somervilles were likewise never higher in rank than a mere Baron, and their title is also extinct now.
> But I do understand something about kingdoms
Perhaps, but not the ones of the pre Norman Conquest of the British Islands, I believe. The families that later assumed the surnames by which wenow designate them had at that time no title in the sense that you seem to envision. Influence in a purely local area, perhaps. Feudal kingship? Certainly not!Unless you want to define kingship as most prominent person among half a dozen (at most) poverty stricken families in one small village. But a first level supervisor of any modern day corporation wields more influence than that and is typically nowhere near CEO status.
> according to my understanding, it's the bloodline that makes the difference. [Correct me if I'm wrong]
Bloodline was but one factor. Military power on the battlefields trumped bloodlines time and time again duringfeudal times, as it always has and that doesn't appear to be likely to change anytime soon.
> I will be researching this more in depth.
You emphatically need to, because of your abysmal ignorance.