Murder charges have been filed against four juveniles, alleged members of a street gang who reportedly killed two men while preying on illegal aliens. Lt. David Lang of the Los Angeles Police Department's Community Resources Against Street Hoodlums (CRASH) unit said two other juveniles and two men also were arrested and held on armed robbery and other charges. The boys charged with murder range in age from 12 to 17. Sabino Martinez, 34, was shot to death after being mugged by half a dozen youths near Norton Avenue and Pico Boulevard on May 9. The next night, police said, Antonio Morales, 25, was killed.