NBC's Miguel Almaguer reports.
Updated at 6:02 p.m. ET: TACOMA, Wash. -- Hundreds of mourners gathered at a church Saturday to remember "two beautiful boys" killed when their father burned their house to the ground with himself and his sons inside.
Sunday's murder-suicide arson, which claimed the lives of Josh Powell and his sons, Charles, 7, and Braden, 5, capped a grim family saga that began more than two years ago with the disappearance of the boys' mother, Susan Powell, under suspicious circumstances in Utah.
The two brothers were at the center of a bitter custody dispute between their father and the parents of his missing wife. Investigators now presume Susan Powell was slain by her husband, though her body has yet to be recovered.
"This moment is about two beautiful boys," Pastor Dean Curry, lead pastor of the Life Center church in Tacoma, an Assemblies of God congregation, said to open Saturday's service.
Braden and Charles Powell
"There have been all kinds of things said surrounding those boys," Curry added. "But what we do here, and the spirit that we do have here, is up to us."
The boys’ grandparents, Chuck and Judy Cox, briefly took the platform to thank law enforcement and others in the community who offered their support "through this trial that we’ve endured."
"Everyone was doing everything they possibly could to keep them safe," Chuck Cox said.
Teachers also shared memories of the boys.
Chuck and Judy Cox express their gratitude to all of those who have given them support.
Charlie Powell’s kindergarten teacher, Tammy Ougheon, remembered the 7-year-old as "an amazing young man" with an appreciation of nature who loved to collect bugs, rocks and plants. "He is safe in his mother's arms," she said.
His younger brother, Braden, preferred cars and trains, teachers remembered, and last Halloween got to dress up as a Transformer. Braden, teachers said, loved to be tickled.
"His little spirit lives on in the hearts of all who knew him," said Kristie King, an instructor at a YMCA that Braden attended.
Many of the mourners wore purple and blue ribbons in memory of the children.
At the front of the church's sanctuary, the boys were in a single casket topped with a large flower arrangement that included daisies, roses and sunflowers. Three screens in the sanctuary showed a photo of Susan Powell and the two boys, all smiling.
Ted S. Warren / Pool via Getty Images
Chuck Cox reaches out to touch the casket bearing his grandsons, Charlie Powell and Braden Powell, as he walks with his wife Judy Cox during Saturday's funeral service.
At the family's request, members of the public were invited to attend the memorial. Curry said earlier he expected as many as 2,400 people to turn out for the service.
A private family interment will take place Monday at Woodbine Cemetery in Puyallup.
Pierce County sheriff's spokesman Ed Troyer said Saturday that Josh Powell's body will be released to a cousin Monday.
Last week, a judge denied Josh Powell's bid to regain custody of his sons, citing the "extreme child porn" found last September in the house he rented near Tacoma.
That discovery had led to the arrest of the boys' grandfather, Steven Powell, who had been living with them and whose vast pornography collection included images of their missing mother. He now awaits trial on criminal charges related to the photos.
The boys were ordered on Feb. 1 to remain in the custody of their maternal grandparents, Charles and Judy Cox, at least until Josh Powell, 36, submitted to a psycho-sexual evaluation.
In this bank surveillance photo released by the Pierce Co. Sheriff's Dept., Josh Powell, left, is seen making a withdrawal at a bank in Puyallup, Wash., on the day before Powell and his two young sons were killed.
Four days after that decision, a child welfare case worker delivered the two boys to their father's home for what was supposed to be a supervised visit. But he abruptly locked her out, then set off a fiery explosion that consumed the house as the worker, herself uninjured, watched in horror and called authorities by phone.
Medical examiners later said the two brothers had suffered chop wounds from hatchet blows inflicted by their father moments before all three died from smoke inhalation.
Pierce County prosecutor Mark Lindquist said earlier this week that he considered "the murder of those children a confession to the murder of Susan Powell" and that he viewed the ongoing investigation into her fate as a murder investigation.
At the time his wife was reported missing, Josh Powell told police he had taken his sons camping in subfreezing temperatures just after midnight on Dec. 7, leaving his wife at home, and that she had vanished by the time they returned that afternoon, according to court documents.
The grandfather, Steven Powell, 62, was charged in September with 14 counts of voyeurism and one second-degree charge of possession of child pornography. Shortly after that, the boys were placed in the custody of their maternal grandparents.
The Associated Press and Reuters contributed to this report.
More content from msnbc.com and NBC News