Harrasment by daughter in law

My brother got married 3 years back, my brother and his wife both are hearing impared in starting phase approx 6 months all was fine, after that period girl is started misbehaving with in-laws and torchuring them but only in absence of my brother.she was having some gyne problem for which my mother took her to doctor,after some visit our doctor make a note verbally- the girl has some Issue related to her mind development,but we ignore that ,she fought and called her parents and they take her away to their home and ask us to allow them some time to let her understand the things , number of time in last 3 years.but nothing changed. Then in our one meeting my mother pointed out the thing that your daughter'smind isnunderdeveloped and you don't informed us at the time of fixing marriage...His father take an appointment with clinical psychologist in government hospitals through his some sources, doctor asked us also to attend every session,we went and after IQ test doctor gave report mentioning that she has IQ level below average. The girl also become violent 3-4 times and scratch my brother.Due to all this my mother is suffering and bedridden from last one year. My brother is also unemployed right now. How can we proceed in these situations