"We have filed a petition seeking quashing of complaints filed against Asaram Bapu and son Narayan Sai," said their lawyer advocate Yatin Oza.
The petition is likely to come up for hearing in a few days.
Asaram, 72, is currently lodged in Jodhpur jail in connection with another sexual assault case while the whereabouts of Sai are not known.
Surat police had recently registered two complaints -- one against Asaram and another against son Narayan Sai -- of rape, sexual assault, illegal confinement and other charges.
The elder of the two sisters has accused Asaram of repeated sexual assaults between 1997 and 2006 when she was living in his ashram in Ahmedabad.
The younger sister has accused Sai of repeated sexual assaults between 2002 and 2005 when she was living in Asaram's Surat ashram.
Ahmedabad police have approached a Jodhpur court to seek custody for Asaram in the present case while Surat police have issued a lookout notice for Narayan Sai.
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