Harassment to mother in law & husband

My elder brother wife has left the home blaming that my mother is torturing her by giving more work where as she was very much cared by my mother & the general household work was divided between her & my sister who is living with us. My mother use to ask him why she is waking late etc… one fine day she left the home by taking all the jewels with his father without the permission of her husband, days have passed & one day we called up for a general sit with few of our & their family members, they blamed with false info & they are not ready to listen us & finally both of the family get apology together & as she was pregnant that time the asked permission to send after delivery & decided that will be kept seperately… we got info of delivery & went to see the child with all our family, they behaved in a very rude manner… after that we came home .. after few days my brothers brother in law came to home to drop her sister in our home & every one given a good welcoming to her & the child … she was quit normal for few days & then started not listening to my mother & delaying in work etc… the same way as she left earlier she left again with her brother… now it has been six month till now she has not returned , kindly advise how this can be tackled legally…