They have been of born in this country since Queen Victoria (her children, not herself). If someones family is resident in a country for over 150 years, they are generally considered to be of that country
Yep, and this is fine for you and me. I am foreign myself but my kids wont be.

My point is that, if there was any potential 'tradition value' it would need the royal family to be the the descentants of a dynasty that spans for centuries...and not a bunch of interbred mostly-germans

As tradition goes they are more akin to bierwurst than to the Excalibur