You query reveals an occurrence of cognizable offences. Therefore in my considered opinion your mother and brother should police station of that area and lodge a complaint with police. If police does not actively pursue the complaint then they should write a complaint to higher police officials detailing incident.

1. Do not keep silence anymore and raise your voice by exploring the legal recourse.

2. So visit a nearest police station and lodge a complaint so a FIR be registered u/s 498A, 406, 326 IPC.

3. Thereafter get a case for maintenance filed by your mother under PWDV Act wherein she can seek damages and compensation as well.

4. So doe not endure the physical or mental agony anymore and file the cases as suggested as above.

There are several remedies available to you.

Start with a criminal complaint to the local police station or the Crimes Against Womens Cell alleging bigamy which is a punishable offence in India. If Hindu Law applies to you then only the first marriage will be recognized by the Courts and the subsequent marriages will be invalid.

Your mother can  File an application for maintainance . Your mother could also file for restitution of conjugal rights which will provide with a court order forcing your father to come back and fulfill his marital and parental duties.

Your mom can file domestic voilence Act against him. Your mom can also file Divorce and maintenance Petition 

Your mother and you all can file a police complaint against your dad for beating and furter ,mother can file for domestic violence and physical cruelty. 

Can seek a divorce and maintenance from father and can stay separately.

Your mother should file DV case against your father seek protection order, maintenance, alternative accommodation compensation for mental torture undergone by her 

1. Why have you not filed a police complaint against him? Do it ASAP. 
2. Your mom needs to file a divorce petition too, to come out of this abusive marriage

Ask your mother and brother to go to a government hospital and obtain medical report which is madatory.Then file 498A, 406, with 307 IPC.

Any kind of abusive behavior by your husband or male partner or their relatives (includes male and female relatives) are protected under Protection of Women from Domestic Violence Act 2005.The DV Act provides that the aggrieved person may approach not only the Magistrate but also the Civil court, Family court or any other courts and seek relief’s including protection orders, residence orders,monetary reliefs,custody orders, and/or compensation orders. The D.V. Act has been enacted to provide a remedy in Civil Law for protection of women from being victims of domestic violence and to prevent occurrence of domestic violence in the society.

Your mother should approach the court and file Domestic Violence case against your father and seek protection order,if need also seek other reliefs like maintenance, alternative accommodation compensation for mental torture.

Dear Madam,

There are several enactments in favor of married women.  Your mother must show heat of the litigation to her husband  otherwise you cannot sustain in such unbearable atmosphere.  

Your mother  better to file Domestic Violence case against your father.

How do I know my husband is subjecting me to domestic abuse/violence?

If your husband is physically beating you, or denying you access to food or money, or is forcing you to engage in sexual activities that you do not want to perform (including sex and something like forcing you to watch pornography) or mentally and emotionally harasses you about not being able to have a male child or any such other behaviour, it is domestic violence. Please look at the definitions section here for further understanding. Further, please look at this Form IV.

Your mother should immediately file a case before police. 

She should move out and file a case of maintenance and claim the same from him. 

Thee is no point in living with him and subjecting yourself to harrasment  

Tell your mom to file police complain. 

A domestic violence case against your father should be filed by you and your mother.

The police shall register the complaint and act accordingly.

Regards 

If your mother is suffering the tortures, she may lodge a police complaint about this and also file a domestic violence case against him.

You help your mother to file the said cases.