Maintenance for baby and wife

My sister got married to guy in 2013. Post marriage, she has been suffering a lot of financial and emotional torture. Her husband and his family had lied to us regarding his income and also hid from us the fact that they had huge debts in the market...around 7-8 lakhs. Due to dis my sisters married life has been full of finacial crisis considering her premarital lifestyle. Moreover she was tortured mentally like being forced to do job, doing both household and office work, no freedom of spending her own hard earned money, periodic expensive desires by husband like smart watch, bike, flight travel which she had to fulfil through her nominal income of Rs.15k else she had to face quarrels and arguments from husband and in laws.Her husband with his meagre income of Rs.28000, which is nt even sufficient in todays world to run a family of 4, is highly extravagant. He wears Ray Ban sunglasses, expensive shoes, often buys expensive smartphones, dslr camera, plays pool on hourly basis, all these habits dont suit a person with so less income and so high responsibility of wife and parents. Moreover he is nt caring at all, even during pregnancy when a girl needs maximum care, love & affection, he and his parents hardly took any care.In fact due to the financial mess my sister had to work till the 6th month of her pregancy even after our repetetive requests to her husband to let her quit job for some rest. Her lifestyle was worst during her pregnancy when she was doing a 8 hr job in office and then all household work like cooking,cleaning. Not a single penny was spent by her husband during her pregnancy or delivery nt even post pregnancy. Even at the time of delivery her husband only came for 2 days despite the provision of paternal leaves in every organisation. I can keep on writing all d small and big incidents but in a nutshel i wud say dat due to all dis my sister finally left her husbands home and came to her maternal home with her 1yr old kid. Its been 8 months she is here and just because her husbands ego is hurt badly due to this bold step, he doesnt send any thing for her or even for his baby. Not even basic needs of a baby like diapers,milk supplements,clothes,etc which even an outsider brings while coming to see him. We have tried explaining him to atleast take care of his babys needs but he refuses or makes false promises every month. And if we ever say anythg to him in loud voice just out of anger for all the torture he caused to my sister...he shows double aggression and attitude. Due to all this we are determined that we would not send her back as now he will do more torture. There are many such things so we want divorce but he refused to give divorce. So we now planing to go for contested divorce but before that we are thinking of sending him a notice for paying monthly maintenance of Rs5000 atleast for his wife and baby. Please advise are we thinking in the right direction. If not then please guide me the best possible course of action.