Hi,

In the same quest phase it is possible to use an hero's capacity (like Jaes one) and a reward (eg: Arcane Ring) if both can be used instead of healing, moving, or training the hero ?

My friends and I think not because you can only use one time an action "instead of" (healing, moving, or training the hero).

No, you cannot; you are only allowed to do one "action" during the Quest Phase, and what those abilities are saying is that using the ability counts as the action in lieu of the regular actions of healing, moving, or training.