The water elves may have been few in number, but it was for this very reason that they were very united. It's not like there were only a handful of them, there were actually thousands, just that, compared to the size and population of the country of Rios, they were few to oversee it completely.
As Sansa had said before leaving, the water elves were known in ancient times as liquid spirits and on par with dragons, they are the race with the largest number of people over a millennium old.
This means that many of their members witnessed and even fought in the war of the lost continent, so just imagine their power. For this reason, when the water elves that Andrew and the others saved told their story, they immediately took action.
Lucas and his friends were not self-centered, nor full of themselves, as they told the events as they had happened, including how Andrew and his companions saved them and what they asked for in return.
