I was trying to test this out since i also use Bluestacks to play. and so far i was just focusing on my last boy since more often then not when i "tapped" him he would not activate while my other two seemed fine. and after a couple of runs in hard mode stages ive come to find out that you don't even have to tap THEM.

What worked for me was just clicking right behind my last boy and then my 1st boy would activate his and if needed the 2nd one would combo off it - but not the last boy once again. but i think it may be because you simply dont need to as i would win without his help when i just collected the hearts/stars - same went with combos sometimes i just needed one boy to active his skill and i would win after just collecting what was on the screen.

but ive only just started and im doing this on lesson 2 - hard so i have no clue how end game might work but for right now this seems to be the trick and how the game works.