Board Thread:Questions and Answers/@comment-32803230-20180211193535/@comment-32271305-20180211205637

Only one of them will transform, if you play badly on purpose in order to last more than 6 turns and also go under 50% HP. The other one won't transform, because the first one will heal you and one-shot whatever is left of the enemy.

This info is all listed on their Wikia pages.