A lot of groups; if not all groups had this problem. At the end of the day it's just the amount of times you smash your head against divebombs until your group of players finally understand it. Divebombs is by far the hardest part of the fight in Twintania, easily.

However, for the 2nd set of divebombs, ensure that your group is kinda' spread so you don't get the stacks from the little adds, in case people DO make a mistake. Other than that, goodluck!