Hang on, guys. You've all overlooked the 7 year rule. The giving away of an asset of this type becomes a 'potentially exempt transfer' for Inheritance Tax purposes. This means that the person who gave away the asset must live for another 7 years after the gift before the value of the asset can be completely ignored for IHT purposes.
Before alarming you further, if the value of your late father's estate INCLUDING the current value value of the house is still less than £325k, you won't have a problem with IHT. If it is worth more than £325k, the ESTATE (not you as current owner of the house) is due to pay some IHT. When probate is applied for, the applicant will HAVE to answer correctly to the question that asks whether the deceased has given away assest in the last 7 years.
The issue as to whether your late father's will includes the value of the house is likely to hinge on when he wrote the will. If it is after the transfer of the house to you, your brothers cannot have a realistic chance of success in their claim. If it is earlier, it is going to depend on the way the will was written (does it mention the house as one of his assets).