Does the property company have the responsibility to change the sewer pipe in the kitchen on the first floor without authorization?

There is no joint liability. Because the owner is the employer of the property management company, the property management company has no right to interfere in the family affairs of the employer. If the drainage of the upstairs residents is affected, the victim may request to remove the obstruction, restore the original state and compensate for the losses. Please negotiate and handle it properly. If consultation fails, the residents' committee may mediate. If mediation fails, or if mediation is unwilling, the victim may bring a civil lawsuit to the court. User suggestions are for reference only. Good luck!