Mother-in-law harassed by daughter in law and son, and husband is baised.

My Middle brother Arun got married 7 years ago. He and both brothers including me studied overseas. His wife, Shalini wanted to go to Australia post marriage but Arun was not interested. And he was also not interested in doing any job, neither does his wife. I being elder brother, single man, kept on sending money for family, for construction and safeguarding of all members property, both agriculture and residential plots in everyone names. Later I started sending money only at sister account after no constructive growth was happening so that sister could action required tasks for parents. When the money crunch started Arun started becoming nasty, aggressive, rumour spreader, intimidating sister, other brother and his family , then me and now mum. Dad was filled with toxic thoughts and fear against sister, mother and me. The underlying reason was to cut off dad from us so Arun and Shalini could mould dad as per their wish which they did. Now dad has become pathological lier, before Arun/Shalini and Dad were calling mum as mental to harass her, and use delay tactics to action her required tasks including getting thing from shops etc. When she make repeated requests the video recording was done and circulated in other relatives to taint mum. As dad was never too attached to mum and been very strict father all life.. it was easy for Arun with the help of Bua Rambeti to mould dad for his own self benefit.Rambeti has long term plan to make dad write everything to Arun and after dad she can snatch it from Arun say 1 crore property by part paying and later do dilly dally to brush him aside. As he will have no strong backing. Rambeti has been emotionally and mentally threatning mum wiith her nasty talks and rumour spreading. Now the issue is I am sitting here at family home to protect mum who was financialy chocked too and with great pain could get some monthly money for her survival. As i work overseas on contract basis and been pouring my saving into family thing. I dont have strong base and cant take mum along with me. And i cant leave her in this situation. How to protect her.. I feel very depressed to see all this. On the flip side Shalini, Arun, Priyanca (youngest brother wife) have been in constant in touch with my brother in law who doesnt work and filling him with negativity to create rift between sister and brother-in-law so she is unable to give helping hand to mum, and mum cant stay at sister place who stays in in-laws house. My dad been lying in his diary to leave trail of bluff against me, sister and mother so if he passes away first then house and all his property goes in Arun control and me and sister cant live here. And mum wont be able to survive without help. and will be tortured day and night. Arun has tried to pressurize mum to sign papers and ask her not to come to certain part of house. The house which belong to dad and Arun and Shalini just living with them. What to do? Dad had brain surgery in 2005, 3 hearth attacks.