叶える （かなえる） to grant (request, wish), to answer (prayer), to fulfill (conditions), to meet (requirements)

叶う （かなう） to come true (of a wish, prayer, etc.), to be realized, to be fulfilled, to suit (e.g. a purpose), to meet (wishes, ideals, etc.), to conform to (standards, rules, etc.), to be consistent with, to match (implies competition), to rival, to bear (e.g. the heat)

叶うことなら （かなうことなら） if possible, if it is in my power, if it was realistic