The quartet - Matt Currie and Damien Hoyland are the other two - have been flown in to assist with training as the Scotland squad ramp up preparations for Sunday's must-win match against Tonga at the Rugby World Cup.
Their brief is to help with training drills and none of the quartet will be considered for the tournament itself. World Rugby regulations allow extra players to train as long as they haven't been involved with the original training squad and wouldn't be called up to the World Cup squad if there were injuries.
Samuel, Brown and Edinburgh centre Currie have all represented Scotland at U20 level while five times capped Hoyland is on the lookout for a new club after nine seasons with Edinburgh.