Do you know if they focus on one piece in the viva voce or whether they do try to ask you something about every piece? I am struggling with prep for the Makholm as there is so little on him available.
They'll probably ask you something on every piece, plus a general 'why did you select this programme?'. The last will be 'and do you have anything else to add?'.
A question on using the score might come up for the Makholm, especially if everything else is from memory.
I had to discuss the formal and tonal structure of that Mozart, the same for a Bach fugue, point out which piece I found the most challenging and how I addressed these issues, and why I'd chosen a particular adjective in my notes (for Shostakovich). Mozart's keyboard will certainly come up.