How come Mark Ballas, Derek and Juliane Hough don't have English accents?

Question

I read they mostly grew up in London.

Answer 1

they were all born in America and later went to London

Answer 2

Mark Ballas was already 12 when they moved to London and so was Derek Hough. I guess they all lived together and in their household, its all Americans rather than Brits so I guess that made them not have English accents. Also, Juliane was only in London for a few years, she had her high school in the US.