My parents want her to change her last name before the wedding, what do I do?

Cancel your train. If you board that carriage while her mother is packing bags and she is sitting silent in the kitchen, you are boarding a life built on an unaddressed ultimatum. You cannot fix a surname dispute from a distance, and a December wedding hall booking is entirely irrelevant if the two people getting married are currently positioned on opposite sides of a family blockade. Go into the kitchen, sit down beside her, and make your position explicit without hiding behind your uncle or your parents. You need to say out loud that you are marrying her, not a name on a reception board, and that your family does not get to dictate her identity as the price of admission. The cost of saying this will be immediate and severe. Your parents will accuse you of choosing an outsider over family honor, your uncle will call you disloyal, and the pressure from extended relatives will spike within the hour. You will face weeks of social friction and possibly an outright breach with your household. Yet the alternative is worse. If you let your family force this compliance now, every future boundary between your household and hers has already been surrendered. Your partner is currently testing whether you will stand between her and an unreasonable demand or let your family absorb her identity by degrees. Let her hear you tell your uncle that the reception board stays as it is or the date is called off. That choice will cost you peace with your relatives today, but it is the only way to preserve the marriage you are trying to build.