"Hello you two."
Translation:Hallo ihr beiden.
"Beiden" is used when preceded by an article, and "Beide" when not.
Lol. Yes, thoroughly happy. :P I've noticed this sort of thing elsewhere, as well, in that it seems "you" plays the role of an article, ... no idea as to whether that's the case, however.
I know this is a bit lame, but I went on Google and put in something simple that Google shouldn't manage to screw up: "You two" to which it answered either "Ihr beide" OR "Ihr beiden", so, ... perhaps it can go either way?
It is my understanding that German has different standards of formality than English and that informal is normally reserved for very close friends and family. I think it would be appropriate therefore to say 'Hallo Sie zwei' to two colleagues or acquaintances who you know but don't know really well.