The girl's were all over Rook because they've likely never seen an alien up close before.
It is a little weird that Kevin and Gwen aren't as famous as Ben, but Ben can change into amazing aliens varying in powers and size, and well, Gwen and Kevin don't.
Yeah, while I don't expect them to be a famous as Ben, but is like Ben is the lead singer, and they are the backup band. The lead singer in famous bands get the bulk of the attention, but the other band members get some left over fame.
Another compassion, in Avatar: The Last Airbender, while Aang is the world savior, his friends still got some fame, they got statutes build for them, in the beginning of season 2, General Fong knew of Sokka and Katara, and even gave them complimentory nick names brave Sokka and mighty Katara.