The burial will take place in their rural home in Thika.
On Monday, Ms Keziah Wambui, the lawyer’s mother, said all was set for the mass funeral.
After the bodies of Allen, 9, and Ryan, 8, were recovered last week, Mr Andrew Kamau, their uncle, said: “We are hoping that police will do thorough investigations to unearth the mystery.”
He said there would be no viewing of the bodies as they have decomposed.
Police are holding a woman, whom they believe has vital information that could help in resolving the puzzle.
Detectives from the homicide unit said preliminary investigations have linked her to the killings.
Ms Margaret Njoki, a househelp, said the woman visited the couple’s house in Muthaiga Pipeline and performed some rituals associated with the occult.
Mr Maxwell Otieno, an officer from the homicide unit, said they are likely to charge her once investigations are complete.
In an affidavit filed at the Kiambu Law Courts, the officer said the woman, a mother of one, was to inherit part of the couple’s property going by a Will handed to an advocate.
The woman was allegedly in constant communication with Mr Magu before and after the killings.
“The woman was very close to my son. He avoided us after we warned him that the woman was deceiving him and would ask him to quit his job to start ministering with her,” said Ms Wambui.
Their little-known denomination did not have permanent premises, she added.