What I would try if I were creating something similar, is store the tickcount at the time of the button press.
So I'd probably have a dummy sprite object with variables I can set, like sprite.button1tick, sprite.button2tick
Then when button is pressed store the tickcount to corresponding variable.
Then have an event that checks if one of the buttons is down, or both, etc.. and also check if their tick variables are within a certain range.
for example: abs(sprite.button1tick-sprite.button2tick) < fps*0.25 & (tickcount-sprite.button1tick <= fps*0.25 | tickcount-sprite.button2tick <= fps*0.25) do action for two button press.
else (tickcount-sprite.button1tick > fps*0.25 & button is pressed & sprite.button1state = 0) do action for 1 button press and set button1state to 1
if button 1 isn't pressed, set button1state to 0.
if button1state = 0 and button pressed, set button1tick to tickcount.
something along those lines..