The pastor of an insular New York church was one of seven people charged on Tuesday with the murder of a young man who wanted to leave the congregation and the assault of his brother.

Lucas Leonard, 19, was beaten to death in October over 10 hours during a “spiritual counselling” session at the Word of Life Church in the town of Chadwicks, New York State.

His brother, Christopher, 17, received blunt force injuries when he was repeatedly struck during the same session, which was being held because Lucas Leonard wanted to leave the congregation, prosecutors said.

Pastor Tiffanie Irwin, her mother, Traci Irwin, as well as her two brothers, Joseph and Daniel Irwin, were charged in a 13-count indictment.

Also named were the victims’ father, Bruce Leonard; their half-sister Sarah Ferguson; and two other church members — Linda Morey and her son, David Morey.

Authorities have said “spiritual counselling” spiraled into an all-night group attack on Lucas and Christopher Leonard inside the Word of Life Christian Church, which serves as both a church and a home for the Irwins.

The indictment charges all but Daniel Irwin with second-degree murder in the Oct. 12 death of 19-year-old Lucas Leonard. All eight face charges of manslaughter, kidnapping, assault and gang assault for the attacks on Lucas Leonard and his 17-year-old brother, who survived.

Traci Irwin was among multiple people charged in regards to the the death of Lucas Leonard and injuries to his brother, Christopher, during an attack at a church in October. Photograph: Mark DiOrio/AP

Joseph and Tiffanie Irwin pleaded not guilty Tuesday and their cases were adjourned until 7 December. The others were expected in court on Wednesday.

Police initially charged six people, including both of the victims’ parents, but the pastor and her mother were not among them.

Oneida County District Attorney Scott McNamara said the victims’ mother, Deborah Leonard, would be charged separately. Her lawyer, Devin Garramone, said she would be arraigned next week on charges of first-degree assault in the death of Lucas Leonard and second-degree assault for the attack on Christopher Leonard.

That would be a reduction from the initial manslaughter charge she pleaded not guilty to in October. There will be no bail, the lawyer said.

McNamara said he could not comment further on the case because of a gag order issued by the judge.

Garramone has said the mother felt helpless to stop an “intervention” that she didn’t expect to become so harsh and he didn’t believe she caused the fatal injuries.

At a hearing last month, Christopher Leonard testified that Tiffanie Irwin asked the Leonard family and some others to stay behind for a meeting after an eight-hour Sunday service. Over what he estimated was six or more hours, he said he was pummelled with fists and whipped with a 4-foot (1.2-metre), folded electrical cord on the back and elsewhere, suffering injuries to his torso and genitals.

Authorities said the meeting was called because Lucas Leonard had indicated he wanted to leave the church. After the attack, the beating victims’ relatives wouldn’t tell officers where to find the injured Christopher Leonard, who ultimately was located on the church’s second floor, investigators said.

The church has existed for 30 years in a rural part of New Hartford, a town of 22,000 people about 50 miles from Syracuse. The church once had about 40 members but now counts closer to 20, New Hartford police Chief Michael Inserra said after the attack.