Your mother would be the legal heir of your brother and would take his entire estate
As she is a class 1 legal heir under Hindu Succession Act, she will exclude all other legal heirs falling outside class 1
For original registered document, your mother needs to lodge a police complaint
As the house is registered in your mother's name, she being the owner, she can do anything she wishes with her property
Her children have no right during her lifetime
If you feel that she will be manipulated, you need to shift where she resides rather than asking her to shift with you
This is what even the courts will say. The court cannot direct your mother to shift with you. Rather it will ask you to shift with her at her place where you can take care of her and discharge your moral duties as child