WHEN ISRAELI AUTHORITIES recently expelled members of the Denver, Colorado-based cult Concerned Christians their dragnets missed at least two key players. NEWSWEEK has learned that Gary and Sheryl Schmidt remain in the country, and Denver police believe that two other cult members are with them. The Schmidts are believed to be the only members who still hold property--they own a ranch in Colorado. Now at least one cult family has been seen at the ranch, and cult experts believe the members may eventually congregate there. Israeli authorities had no comment on their investigation.