Beyene and Calderwood, who are charged with conspiracy to rob and firearms offenses, were flanked by five security officers as they appeared in court. They spoke only to confirm their names, addresses, and dates of birth.
Defense lawyer Antonie Xavier, who represents Beyene, said his client "totally denied" involvement.
"He has always denied that he was ever near there," Xavier said. "This is a shot in the dark."
Later Friday, police announced they had charged a third man with conspiracy. Clinton Mogg, 42, of Bournemouth in southern England, is scheduled to appear in court Saturday.
The Aug. 6 robbery at Graff Diamonds in the upscale Mayfair neighborhood grabbed headlines in Britain and drew comparisons with movie plots.
Two well-dressed men walked into the tony shop and pulled out handguns, ordering a member of staff at the upscale jeweler to put 43 items into a bag. Watches, rings, bracelets and necklaces were taken, with a retail value of more than 40 million pounds ($66 million.)
The Metropolitan Police declined to say if any of the jewelry had been recovered. A third man arrested this week remains in jail.