"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 younger sister has accused Sai of repeated sexual assaults between 2002 and 2005 when she was living in Asaram's Surat ashram.
City 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.
