P = V^2 / R. first things first V (voltage never changes). in a parallel circuit, R (resistance) doubles at the power source but not at the R source (speaker). the resistance at the speaker will never ever change. therefore, if u see a 2 ohm load at the power source (P=(V^2)/2) based on two 4 ohm speakers wired in parallel those speakers are still 4 ohm and being that the voltage will not change, they will still see P = (V^2)/4. no any number divided by 2 is two times greater than a number divided by 4. and being that V never changes. wallaaaaa
second, to wire those speakers to a 2 ohm load. the voice coils of each speaker need to be wired in series first to make 4 ohm speakers, then the two speakers need to be wired in parallel to create a 2 ohm load.