I would suggest hiring a solicitor if he does actually follow through with this threat. Typically, the bulk of an estate would go to the surviving partner in a marriage / civil partnership with children or dependents having a greater right to any further estate above a certain threshold, long before a brother would have any real entitlement. Any property held in both your father and mothers names wouldnt form part of the estate. There are subtle variations depending on what part of the UK you are in; but for example - in England, the estate would be subject to intestacy rules; meaning the first £270k would tend to go to his wife (your mother).