Sicily has signed a three-year contract extension, locking him away until 2020, while O’Brien has signed a two-year deal which will see him remain at the club until at least end of the 2019 season.
The pair signed new deals on Tuesday afternoon, with both players enjoying their career-best seasons in 2017.
Sicily is averaging 17.8 disposals, 6.6 marks and 2.4 rebound 50s from 18 games this season, and has recently starred with a move to the backline.
“James is an exciting player to watch,” Hawthorn’s Recruiting and List Manager Graham Wright told hawthornfc.com.au about Sicily.
“His passion and determination is on display every time he plays, and he’ll continue to hone those qualities as he develops.
“He plays an important role within our young backline, and we’re looking forward to seeing where this emerging group of players can take us.”
O’Brien has also enjoyed an impressive 2017, as his 15 games have seen him average 10.3 disposals, four marks per game, while also booting 18 goals for the season.
“We can see a really promising future for Tim in the brown and gold,” Wright told the club’s website.
“He’s shown some good signs this season, particularly as a strong marking target up forward and the role he has been as a backup ruckman.
“We’ve got a number of talented youngsters coming through our ranks, Tim included, so we’re excited to watch our list develop and see what we can achieve in the coming years.”