Here, is 'you two' a fused-head NP with 'two' being a determiner-head?
If not, how should the NP 'you two' be analyzed?
"Two" is the (fused) head of the phrase. It is a determinative which takes over as the head of the NP for the understood noun. The noun referent "people" is left out (or guys, or dickheads..or any other noun that can be understood as having a personal referent) simply because it is too obvious to justify mentioning (however, it may add some new information that might tell more than simple "you two people". "People" doesn't contribute anything information-wise - of course they are people. On the other hand, "You two dickheads" says significantly more than just "you two")
"A SINGLE word (a determinative or adjective) is at the same time a determiner or modifier and also the head". (A Student's Introduction to English Grammar p97). In other words, what is understood as the fused head of the phrase is not "you two", but rather just the determinative "two".
The word "you" in "you two" should be analyzed as an external dependent in the NP - a determiner. It makes the nominal definite in the same way the demonstratives do, for example. (Those women and you two guys are the favorites for the award.)
So, for example, the question "Which of the four of us?" might be answered with "You two", where "you" serves the purpose of identifying the persons in question.
"You two" is not a case of apposition, although the concepts of "definitiness" and "reference-specifying" do overlap partly. Apposition is to be understood simply as "naming". Most often the appositive NP literally names the previous NP referent - refers to it by a proper name.
CGEL (p374) gives a couple of properties distinguishing this construction from apposition. The striking point of difference is obviously the fact that we have only plural you and we/us in this construction. This means that the following head has to have a plural referent. (I think that a case could be made for "them" as well: I hate them crazy weirdos.) No such restriction applies to the use of appositive NPs.
Even with plural referents the two constructions will be distinguishable. To take the examples from CGEL:
We supporters of a federal Europe will eventually win the argument.
We, the supporters of a federal Europe, will eventually win the