Father's family torturing mother and not giving enough maintenance

My father is a 50 year old man.My mother and father are married for 27 years now.He along with his siblings had tortured my mother for many years.But my mother still lived with him.But now when she told him that he has to choose between his siblings and family,he just said that at any cost he would not leave his 5 siblings.He earns ₹60000 per month and only gives ₹6000 to us.We are 3 brothers and 1 sister along with my mom how would be suppose to live in a big city as Jalandhar in only ₹6000 per month?He tells everyone that he gives ₹50000 to us which is a lie.What my mother should do now?We are Hindu.If divorce is the only real possibility now so in what cost it would get done if they both agree for divorce.Or is there any other alternative?w