When using prestige bonus during two player, can I choose Consume VPx2 as my second action?
The prestige bonus card applies only to one phase card:


  In the 2-player advanced game, place the prestige/search action card and the action card for the other phase you selected, naming the phase receiving the prestige bonus as you flip your action cards over.


So... you get exactly the appropriate bonus for the phase you choose to apply it to. It's easier to look at the nice pictures in the rules, but there are text descriptions as well:


  Consume: Trade
  
  Sell a good, drawing 3 additional cards; then consume any remaining
  goods doubling the number of VP chips received (as the Consume +x1 bonus
  applies) and, optionally, discard up to two cards from your hand for 1 VP
  apiece.
  
  Consume: 2x
  
  Triple (not double) the number of VP chips (only) that you receive.


So the most VP you can possibly get is 3x (by applying it to the consume 2x), and if you want to get fancy trade bonuses (by applying it to the consume trade) you'll get 2x VP.

(Note that in both cases, the prestige card adds 1x VP. It doesn't actually say 2x or 3x on the card.)