Palafico round in Perudo
Good question! I agree that the rules aren't completely clear here. We play this by treating the aces in a palafico round exactly as if they were normal numbers. So in your example both two twos and three twos would be valid bids by B. 

Think about the purpose of the doubling rule for wild aces. In a normal bid, when you say five threes, you are making an estimate about the number of threes plus the number of aces. But when you bid on aces, you are bidding on aces alone. The doubling rule exists to make these bids comparable.

But during a palafico round, aces are not wild; they're just ordinary numbers. It thus doesn't make any sense to require the doubling rule, because in this round, no bids benefit from additional aces. In other words, all bids are made on equal terms.