You will be facing three waves of 3 antelopes each. Once you are down to a single antelope, the next wave will spawn. In order to succeed, it is vital you keep the NPCs alive, but just curing them will cause them to take damage faster than you can heal. The trick is to help kill one of the antelope, so it's no longer harming the NPC, then focus on healing the other NPCs.
On the second wave, in addition to the antelopes there will be a water sprite that targets you. This enemy hits hard, but doesn't have a lot of HP, so it should be dealt with immediately. On the third wave, there will be two water sprites. Take care of your enemies, help with the antelopes, and keep your comrades alive and you will succeed.