This is a complicated situation. It may be difficult for your mother to leave your father. She might be frightened of him. He may have warned her about leaving. If she did leave, he might follow her and physically harm her. Despite the abuse, there may be a part of her that doesn’t want to leave. It is important to have a discussion with her about the possibility of leaving.
If she is willing to leave, could she live with you? If she can’t live with you, there may be other family members with whom she could live. Domestic violence shelters may also be a possibility.
I am not familiar with Ireland’s mental health system or criminal justice system but you should explore your mother’s legal rights. Perhaps she could gain an order of protection (also known as a restraining order) against your father. In America, an order of protection attempts to prohibit an individual from engaging in abusive behavior toward another individual. If violated, the individual who refuses to comply with the order faces criminal charges.
Encourage your mother to call the police if your father physically assaults her. In America, if the police are called to the home during an abuse incident, the individual who has been identified as the abuser would be arrested. Consult a lawyer or local police officers to determine what other legal rights your mother has.
I hope that your mother is able to remove herself from this abusive situation. It may be difficult for her but she should still try. She is lucky to have a daughter who is willing to help. I wish you and she the best of luck. Please take care.