This might be a good thing actually. If they're both trying to pull the same sad scheme then they probably won't rat each other out.
Unless we go by high school mentality. The first one to rat the other one out actually gains the benefit of "fitting in" and able to be the "cool" one. It's basically a prisoner's dilemma at this point.
The question only goes to has the dark elf established herself enough to be part of the class, or is she just as new as the Elf.
Or is this just a regular occurrence in this world (I doubt these two are the first to try, seeing as how Elves in Bb's world aren't known for their Int build) and all of this is just another day for the poor people in the school, waiting for the Authorities to come and and nab these sneaky elves.
That school will probably start getting suspicious when several dozen elf "students" suddenly show up.
Well, not. Because generations change asynchronous with various regions and that bunch of elves was "just about the age" to roll in. Suspisions shoud raise when they start diggin' up "time capsules" or checkin' archives.
Now that's the twist that could make this work. Start with them simultaneously scheming to get into the boys' pants but distracted by scheming to get the other girl to slip up and reveal her real age (can't just go reporting them to the authorities, of course, or you'll get caught yourself), culminating in their shenanigans almost getting both of them caught.
Then, they agree to a truce, and decide to pretend to make out with each other to try to lure boys into a FFM threesome. It never works the way the intended (this being a baalbuddy universe, all the dudes figure "they're lesbians, they won't be into guys"), but they find themselves getting into each other, and so by the time they do finally get caught and kicked out, they don't care.