Justice for my sister and her son

My sister is married since 17 years and stayed in her joint family.she has a 10 year old son who is suffering from ADHD syndrome and a mild dyslexia. all went well till then but 6 years back my brother in law fell in bad company and took up to heavy drinking (first it was in limits) and other vices. my parents approached his parents to check on him but they cut relations with us. after this episode my brother in law grew careless and started harassing my sister by bad mouthing her in front of her family and son and he drank to to the extend that he was bed wetting approximately 4 times a week. my sister constantly complained for almost 1 1/2 year to her family to help her out. her father in law ignored the whole thing saying its her duty to clean up her husbands mess. her brother in law was a bit helpful and used to understand her problems and insisted that his elder brother should mend ways. since 7th september 2014 my sister has left his house since she was tired of struggling with her husbands bad temper and bad habits. she decided to focus on her sons medical requirements of multiple therapies required daily and improve her sons life. her family have not financially supported them since she left the house and have not even invited her son to their place when they visited his city in school vacations for almost 2 months. we have a feeling that her in-laws do not want my sis and her son back since her son needs occupational therapies and special educator regularly. the way her father in law supported in her husbands misdoings we feel he had malice plan of removing my sister and her son as now he does not want to support them financially. they have not taken any concrete steps to take my sis back nor are giving the gold and silver which my parents had given to my sister in her marraige as well as during this 17 years on different occasions. my sister is totally dependant on us financially and her son needs extra than normal children. we are feeling cheated and have a instinct that they are not interested to take her back as they feel that it is expensive to maintain the child and they have indirectly told us to create a fund for my sister and her child. what steps should we take??? my sister is afraid to go back as they have been mentally harassing her and her husband cannot mend his ways. can we get our gold/silver back. her father in law used to tell her that it is easy for any male to remarry a girl from an 'ashram'. we think they know that my sister is scared to go back so they do not demand divorce but do not sort out her problems too and have decided to get rid of her and their grand child by not giving her any financial aid. they are very wealthy have lots of ancestral property and ornaments etc. now they are saying that my brother in law does not earn so my parents should look after my sister and her son. we feel very bad that my sister has tolerated enough to save her marriage and has gone through lots of mental harassment . they have looked after her till they were interested and now her father in law or mother in law have not approached them since 10 months nor have looked after their needs. my brother in law could have changed if his father had listened to us but he is the one to pamper him and damage my sisters life. now they say my brother in law has sold my sisters gold. a girl does not have right on her parents given gold ?? they are planning to remove her empty handed with her child...please help us.