The paradox of the Bodhisattva Path (Bodhisattvayāna)
There is no paradox.  Rather, it seems there may be some mistaken assumptions behind your question.
First, if someone is enlightened that does not mean that they will enlighten all people. For example, The Buddha was enlightened and yet he did not enlighten all people.  In fact, after his enlightenment, he actually wondered whether he should teach what he learned to others!
Second, no one can enlighten anyone, they can only help or hinder people on their quest to enlightenment.  Whether someone gets enlightened is up to that person.
Third, you don't need to be enlightened to help others on their quest for enlightenment.  For example, I am not enlightened, but I can still explain the benefits of mindfulness to another person.  This can encourage the other person to try mindfulness practices, and this can set them on their journey to enlightenment.
Finally, a Bodhisattva chooses to forego Nirvana in order to aid all sentient beings.  Depending on which definition you go by, this aid can be mundane -- such as feeding the hungry, reducing pain, etc... Or it can be sublime, such as aiding people on their quest for enlightenment. Either way, there is no paradox here; the Bodhisattva chooses to be reborn.