The thing about Fronts is that they have to be directly compelling to the the characters. Otherwise, the characters have no reason to pursue them than "because the GM said so" (something "works" in other game systems.

Now, the players has already said what was interesting to them: the competitin between the Ranger and the Druid, and that the island city is a center for trade and technology.

I didn't see anything about Elves in any of that. So, I can't help but think they are being introduced because you are interested in including them. There's nothing wrong with that, but you also need to make sure that is interesting to the players, as well. Why? Because the characters have option of ignoring any Front or adventure element that isn't interesting.

Ideally, the time to do that would have been in the first session, using some leading questions about what the characters had heard about elves in the area and how they considered them a challenge to the city.