Ok so i had ral zarek and Chandra the firebrand on the board and I was attacked with no blockers towards my PWs. Do I get to choose which takes damage or does my opponent?
Your opponent chooses when he attacks which creatures attack you, which attack Chandra, and which attack Ral. Damage of a single creature can't be split.
Your opponent decides which planeswalker(s) they are attacking when they attack with their creatures. They can choose to attack both of them or one of them, whichever they wish. The defending player does not get to decide which of their walkers gets attacked.
508.1b (http://imtgapp.com/forum/index.php?action=imtg;area=rule;number=508.1b): If the defending player controls any planeswalkers, or the game allows the active player to attack multiple other players, the active player announces which player or planeswalker each of the chosen creatures is attacking.