What did the Grapevine staff decided to write about ? Why ?

Together, the three students decide to publish an issue of The Grapevine that is critical of The Wave. They schedule an emergency meeting at Laurie’s house.

who are the three students , Why they decided to write ?

Those would be the staff of the school paper, I don't recall their names. They see the damage the wave is causing to student psyche. 

Their names were Laurie Saunders, Carl Block and Alex Cooper. They decided to put an issue out because they realised what The Wave was doing to the students and they had to put a stop to it.