ok, here we go again:
the twin linking of YOUR army's weapons, etc, applies to YOUR ARMY (ie: what YOU have taken on your list, which constitutes half the team). your teammates army is NOT YOUR ARMY. it's that simple.
as far as an allied unit gaining the benefits, it's unbelievably vague. i would have to say that they do benefit from it, but also completely disagree with the logic behind it.
the chooser of the slain works against INFILTRATORS. im pretty sure that even though a unit may have the rule INFILTRATE, it isnt infiltrating when it OUTFLANKS. i would, under any circumstance, define an INFILTRATOR as a unit which is actively using the INFILTRATE rule as it is defined in the codex, not as a unit which simply posesses it.
(caps for emphasis)