If you use two Pokemon with Pressure in a double battle,how much will the PP usage increase?

Question

Will it be -4 or -3 or something else

Answer 1

Well the definition on pokemon database is

Pressure makes any attack targeted at this pokemon - regardless of whether it hits - use 2 PP instead of 1.

But it actually uses 1 PP extra for each Pokemon with Pressure. Any moves that target multiple Pokemon with Pressure will use more PP, for example Heatwave (both opponents).