How to deal with the relationship between Party B and Party A's property manager?

First, don't come to a conclusion directly when encountering similar things. After all, you are not the decision maker.

Second, we should think from each other's point of view and try to solve the problem together in attitude;

Third, see how to realize their requirements and what problems exist;

Fourth, which problems you can handle yourself and which problems you can't handle, please ask them to handle them or other departments to handle them.