unconfirmed bigamy

My mom married my dad after she separated with her first husband whom she had one child. Mom found out that her previous marriage was not forwarded to NSO so they entered my mom's second marriage(with my dad) then my mom and dad separates...my dad's second wife wants to marry my dad so they look for my mom's unregistered marriage at the LCR and forwarded it to NSO so to make my mom and dad's marriage null and void. Is there a probable cause to file a case against my dad and his second wife for doing this? Does forwarding my mom's first marriage a legal act to void an existing marriage? Thanx