First of all, the 120mb international data plan is not shared data. You would need to add it to each line in order to avoid data roaming charges or turn data roaming off on each phone. Same thing for the international text plan, it is not shared. If you don't plan to text much, it might be cheaper to just pay the 50 cents per sent text (incoming texts are free).
Your assumptions about data when on the resort's wifi are correct.
Your assumptions about data when on the resort's wifi are correct.