Simplify the following text for a Grade 7 native English-speaking person.
Original: Koror developed a core group of five : Tom , Ian , Gregg , Jenn , and Katie , and those on the outside saw them as a threat but were not able to break them .
Simplified: Koror had started a main group of five : Tom , Ian , Gregg , Jenn , and Katie , and those on the outside saw them as a threat but were not able to break them .