Quarralsome lyingdemanding wife who keeps going to her mothers house and threatns with suicide if io

My brother got married in 2010 and has a 9 yr old son. his wife is very quarrelsome always wanting lavish lifestyle. lies a lot and is abusive towards her inlaws and my brother. every few months she wants to go to her mothers place to stay for months.always demands money and separation from the family which comprises of our elder brother and his wife and children. she only wants to keep relations with her own family.refuses to have another child although my brother wants it. denies maritial relations.only wants to spend money lavishly .this time she went to her mothers house without consulting my brother. uses her son as a blackmail weapon. brainwashes him against even his own father. lies that her husband hits her although its the other way round. her own family also don't say anything to her. she had even filed a complain in a police station against my brothers saying that they had beaten her although she was the one who raised her hand on both my brothers.this time when my brother objected to her visit to her mothers house again she threatened him with suicide. we all are fed up of her. how do we save our family from her,. she has no limits