The father, 41, was stabbed in the stomach, arms and neck. The son, 20, suffered a single stab wound to the chest.

The pair were taken to Westmead Hospital for emergency surgery. Their conditions have since improved and they are both in a stable condition, police said.

More than 30 people were involved in the brawl outside Rouse Hill Town Centre about 8.30pm, which a witness said was arranged following an argument on Facebook.

Police were called to the intersection of Caddies Boulevard and White Hart Drive, following reports of the fight.

Police say a knife, a pair of scissors and a baseball bat were seized.

The Hills Local Area Command Inspector Jim Szabo would not divulge the identity of the victims, but said police had information the fight had been brewing for a number of weeks.

"It wasn't a random attack," Inspector Szabo said. "We will allege it was an organised fight between the parties involved. We're alleging that both parties were aware of what was going on over there and they both went there with the knowledge that there was going to be some sort of incident.

"Be very mindful that things of this nature can happen where people end up in a serious conditon and they can be assaulted with weapons."

Police are unsure how the accused men fled and were unable to confirm witness claims that the fight was incited by a Facebook argument.

"We would strongly advise anyone who wants to go and see a fight on social media to avoid it for their own safety," Inspector Szabo said.

The witness said the father took two of his sons to Rouse Hill to confront another man who was "trash talking" one of his sons on Facebook.

It is unclear whether this was the same person who allegedly stabbed the pair.

"It was all fists and then they starting picking on other guys and jumping them," the witness said.

"I saw one of the guys who got stabbed running off but then he collapsed to the floor. The guy who had the knife just went away.

"There was a lot of blood. The knife was the length from the palm of your hand to your fingers."

It is understood the two groups from the Quakers Hill area were brawling for less than two minutes before the alleged stabbing occurred. From then, both parties left quickly.

The witness said the injured teen asked him to record a video message on his phone to show his girlfriend if he did not make it.

"I was the only one with a working phone so he asked if I could record a message in case worst came to the worst."

A short time afterwards, police arrested five males at a home in Woodstock Avenue at Whalan.

They were taken to Mount Druitt police station.

The three brothers were charged with two counts of wounding a person with intent to cause grievous bodily harm, and affray.

They were refused bail and are due to appear in Parramatta Local Court on Friday.

Anyone with information should notify Crime Stoppers on 1800 333 000 or at nsw.crimestoppers.com.au.

- with Daniel Fallon