Saville, 20, moved to Griffin Park in the summer and has played 24 times for the Bees, scoring three goals.
Trotta, 21, has scored seven goals in 20 outings for the Sky Bet League One leaders since joining the club in September.
"George and Marcello have made an excellent contribution to the season so far," Bees boss Mark Warburton told the club's official website.
"I have every confidence that they will continue to have a very strong influence in future games.
"Thanks to Chelsea and Fulham for their co-operation and we look forward to seeing them develop in the months ahead."