The problem of real estate had better be related to lawyers.

According to the relevant provisions of the property law, this house should be owned by your father. Four years ago, when your father reached a house sale agreement with them, the contract was deemed to be established. Now A's remorse can be regarded as breach of contract, and he can sue to the court for compensation. You can ask A to complete the remaining procedures and complete the house transfer procedures; You can also ask the court to evaluate the house and compensate you according to the market price. You can buy another house, or you can ask him to pay for the decoration, the labor cost of moving, and so on.