Yes - as a Gold you definitely can use the extra availability (V Class) and the Gold Priority Reward to book tickets for others, even if you do not fly yourself. I do this the whole time. It's one of my favourite Gold benefits - most recently, using this to send Mrs R to Italy for the weekend using a GPR instead of paying c. £400 for the dates and times we need.

The situation you describe is different and, I agree, not possible - you cannot even within a HHA use the extra availability of Gold Passenger A to combine with a 2-4-1 of Non-Gold Passenger B....

In fact, even as a Gold with your own 2-4-1 it's a little restricted - you can, I am pretty sure, still use your own 2-4-1 to access the extra availability "V" fare classes (sure I have done this), but you cannot apply a 2-4-1 to a Gold Priority Reward booking for two passengers.

All of this is in the small print - always worth knowing before you pick up the phone as not all call centre staff (even on the Gold line) always know the detail.