They join recent signings Cale Morton, Jack Grimes, Stef Martin and Addam Maric, who have also penned new deals for 2010-11.
Skipper James McDonald is also on board for 2010.
The news comes on the heels of the Demons reaching an in principle agreement with Carlton to acquire selection No.11 in this year's NAB AFL Draft, with the Blues gaining midfielder Brock McLean.
Sylvia, 23, had his best season in 2009, playing as a midfielder/forward. He notched up 17 matches, which included a career-best 37-disposal and four-goal appearance against Hawthorn in round nine.
Taken at No.3 in the 2003 NAB AFL Draft from Bendigo Pioneers, Sylvia has played 87 matches since debuting in 2004.
Although injuries have interrupted his career, Sylvia stepped up considerably in 2009 and is an important part of the club's future.
Injuries ruined Wonaeamirri's season in 2009, with the exciting small forward sustaining a hamstring injury in Melbourne's NAB Cup clash against Hawthorn at Launceston in February.
He then suffered a knee injury via his comeback with Casey Scorpions and was sidelined from round seven for the rest of the year.
It made for a frustrating season for Wonaeamirri after his impressive 2008, which included 24 goals from 18 matches after starting last season on the rookie list.
Wonaeamirri, 20, was drafted from Darwin via Norwood in the December 2007 NAB AFL Rookie Draft.
Melbourne list manager Tim Harrington said it was great that the duo was staying at the Demons.
"We have a promising group of young players, and they are an integral part of our future," Harrington said.
"Colin stepped up considerably in 2009 and showed us what he is capable of on a more consistent basis. Austin struggled with injuries but, after a full pre-season, we are confident that he can make a strong impact in 2010."
