Consequences of son as witness in father's WILL

Sirs, 1) I am a Hindu. My father passed away few years back in Mumbai. 2) He has executed a handwritten Will duly signed and dated. I, his son and an independent friend attested it as witnesses. 3) In the will he has bequeathed all his properties, bank a/cs & FDs and other assets only to my mom. Thus, my mom is major beneficiary. 4) Only a vehicle has been bequeathed to me. 5) There is a very high probability of this will being challenged in court. 6) My query to all esteemed lawyers is whether this Will is valid by law and winnable in court? Regards,