She alleges the boys got away with about $200 Sunday night. Police say the other two boys, also 15, waited across the street and acted as lookouts.
Officers say they recognized the brothers from surveillance video and arrested them Monday along with the two friends. All four were charged with first-degree robbery Thursday in King County Juvenile Court.
Court records say the 15-year-old accused of holding the pellet gun had talked about robbing a different store but the boys thought the clerk who worked there was "huge." Documents say they decided on the gas station because the clerk there was a "short, scrawny guy."