By Mark Maurer The five elevator buildings offer 289 units and 199K sf in air rights A group of real estate investors led by Joshua Sternhell and Mike Spira is in contract to pick up five Washington Heights rental buildings known as the Fort Riverside portfolio from Sentinel Real Estate Corporation for $101.5 million, or about $300 per square foot, sources told The Real Deal. The six-story elevator buildings contain 289 apartments and span 341,148 square feet. They are spread