Police found six people, a man and five children, between 18 and 25 in a small ground-floor room.
A 67-year-old man arrested on Thursday was one of six found on Monday's property. by the police. They all claim to be members of the same family.
"The suspect is believed to be the father (s), the other five, and the person reporting the case is said to be his children," police said.
The man and six grown children may have lived in the house separated from the community since 201
"We have reason to suspect that the six people involved did not stay in the house … of their own free will," the police stated. "We are investigating whether a particular religion or philosophy forms the cause of their life situation."
None of the six children registered but in a national database, and police said they were trying to determine their exact relationship with each other.
Aerial photos of the property show a tree-lined farm with three buildings and a vegetable garden.
The 58-year-old, who was also not baptized, was arrested on Monday. Police said he rented the house and was initially detained to thwart a police investigation, but is now "also suspected of being an accomplice" with the 67-year-old man.
Both men are also accused of money laundering. , and the 67-year-old has also been charged with "abuse in the sense of harming the health of others," police said in English.
The Dutch police called it a "unique situation" and an "exceptional case". They said the experts were helping the young adults who were found, and that all six were already in safe rooms.
"We understand there are many issues," police said on Thursday. "We are carefully examining the question so that we can answer as many of these questions as we can – held by us."