about cross FIR

Dwakra group members(women) are file a FIR against my friend under section 509.
Actually what happened , "my friend's mother was secretary of this dwakra group. The dwakra group leader is not pay the money to the bank since 6 months.
My friend's mother is go to the muncipality with the help of my friend because she was not able to walk. Her legs are not supposed to walk. She is complaining against leader of the dwakra group to the head of the dwakra group in the muncipality. Head of the dwakra group was warned to the leader of the dwakra group to pay the all the money to the bank
After 20 days leader and members of the dwakra group(except my frds mom) file a FIR against my friend,"that is he abused all the women and try to give them with a Rowdy in the muncipality.
I promised really he was very innocent and he didn't abuse them.
My question is 1 why they didn't file a case against my friend's mother and 2 why they file a case against my friend and 3 now can we file a cross FIR against them. If the police investigate this case I definitely said my friend is proven with clean chit and with a good conduct.
My friend has got married newly and he has two months baby child so if my friend was in trouble they are difficult to survive.
So how can we file a case against them in the police station to investigate this case on both sides. And now we can file a FIR against them with my friend or my friend's mother? And they have the rights to file cross FIR againt them or not?