They are all being quizzed at the circuit house here, CBI sources said.
Osian MLA Maderna is under judicial custody, while Luni MLA Singh is skipping questioning for the past several days despite repeated summons.
The probe agency may seek his arrest warrant today.
The agency has questioned Singh's sons a few times to know the whereabouts of their father, who had sought exemption from questioning on heath grounds till last Friday by moving an application in the court, but he did not appear before the CBI team so far for another round of questioning.
Bhanwari, 36, posted as an auxiliary nurse at a sub-centre in Jaliwada village, is missing since September one.
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