Posible options in my mind:
a. The tokens enter at the same time, but the rally ability only counts there being two creatures on at once: The Ondu Cleric, and the token who activated Ondu Cleric's ability. This happens twice, so 22 is 4. (Didn't seem likely, but hey, this might be the case)
b. The tokens enter one at a time, and the rally ability gives 2 health, then 3 health for a total of 5.
c. The tokens enter at the same time, and the rally ability counts 3 creatures both times it is activated for a total of 6 (23).
Optional Question: What if I started with 2 Ondu Clerics on the battlefield? Would that just double the health gained, or would something else happen?