Police said Sean was driving unlicensed when his car hit a wombat before swerving into an embankment and flipping close to midnight on Friday at Munghorn, near Mudgee.
Sean was thrown from the car and suffered serious head injuries, while Jackie died at the scene.
The teenager was air lifted to Westmead Hospital in a critical condition and died on Sunday morning.
Tributes have started pouring in for the young men online.
Leigh Cottee posted on Facebook: “To my beautiful nephew Jackie Omalveney and his best mate Sean may the 2 of u fly high and watch over us now and forever”.
Another friend, Jacki Kovas, wrote: “2 young boys gone way too soon. Sean Lucas you were one of the funniest cheekiest boys I’ve ever come across . Will never forget the times spent with you”.
Jackie’s mother, Leonie, has set up a GoFundMe page, that has raised over $3000, “to help raise money to bury my 14 year old son who died tragically in a car accident”.
Metropolitan Crash Unit officers are investigating the crash and a report will be prepared for the Coroner.
Meanwhile, NSW police have urged motorists to slow down with three people dead and more than 3000 drivers clocked speeding over the long weekend.
Police said there had been more than 140 major crashes across the state, with 50 people injured.
“Speeding is a risk that can lead to a tragedy. Drivers need to slow down and remain alert while on the road. I urge everyone to take care, drive responsibly, respect other motorists and obey the road rules,” Traffic and Highway Patrol Commander Assistant Commissioner John Hartley said.