The victims' uncle and two others were produced before a duty magistrate after expiry of their three-day police custody.
The court remanded them in judicial custody till March 20 after the Delhi Police said that they no longer require the trio for custodial interrogation.
Police had arrested the siblings' uncle Amit Singh, 22, and his friends Shivam Gupta, 19, and Pankaj Kashyap, 19, for kidnapping and murdering the two kids. Their fourth associate Abhishek is yet to be arrested.
The police had said the four accused were eyeing on Rs 30 lakh which the family had got in a property deal a few days ago. Being their relative, Singh was aware of the deal.
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It had said that the accused had tried to kidnap both the children on a previous occasion on February 23 but could not do so as they were absent from the school that day.
Singh had finalised a deal for buying a flat in Mandawali and needed Rs six lakh for clinching it, it had said.
Kashyap had lost heavily in gambling and had debt of Rs 1.5 lakh and needed money to repay it, police had said, adding that Gupta and Abhishek needed money.
Kashyap, Gupta and Abhishek were to get a share of Rs two lakh each and the rest was to be kept by Singh, it had said.
After Singh "confessed" to the crime, he and his two accomplices were arrested, police had said.