A 61-year-old is facing a further charge of indecent assault, and a 73-year-old faces a further five charges of indecent assault.
All four men will appear at Auckland District Court on Tuesday.
None of the men continued to be connected to the school, Dilworth Trust Board chairman Aaron Snodgrass said.
"The board deeply regrets and apologises that some of our old boys have suffered abuse while in our care," he said.
Dilworth School had been working actively to support police in its investigation and encourages former students to lay a complaint if they have been victimised, Snodgrass said.
"We have been determined to confront honestly and openly what has happened and make sure that we do everything in our power moving forward to create and maintain an environment where our young men are safe and where they flourish."
The school is offering support services for the victims, but said its focus was on "the wellbeing of current students" while supporting the wider Dilworth community.
The additional arrests and charges come weeks after the third death among the accused men.
Keith William Dixon, 70, had been living in Palmerston North before he died.
Dixon was charged with offences allegedly committed in 1973 and 1974.
Rex Clarence McIntosh was facing seven charges of indecent assault in relation to five boys between 1972 and 1980 before he died in hospital, battling pneumonia and kidney disease.
His death follows that of Richard Charles Galloway, another one of the nine men who have been charged as part of Operation Beverley, the investigation into historical sexual abuse at Dilworth School.
Galloway died on November 26 aged 69 after earlier being diagnosed with cancer.
In March, former Dilworth house and scout master Ian Wilson was sentenced to three years and seven months in prison for indecently assaulting five students between 1975 and 1992.
The 69-year-old said through his lawyer during sentencing that he was remorseful for his actions, but was introduced to "degenerate" behaviour at the school.
Five men are still going through the court system, including Ross Browne and Alister Harlow.
Others have been granted name suppression.
Police claim to have now spoken to more than 150 former students of the school as part of Operation Beverly.
Where to get help:
• If it's an emergency and you feel that you or someone else is at risk, call 111.
• If you've ever experienced sexual assault or abuse and need to talk to someone call the confidential crisis helpline Safe to Talk on: 0800 044 334 or text 4334. (available 24/7)
• Male Survivors Aotearoa offers a range of confidential support at centres across New Zealand - find your closest one here.
• Mosaic - Tiaki Tangata: 0800 94 22 94 (available 11am - 8pm)
• Alternatively contact your local police station.
• If you have been abused, remember it's not your fault.
