I'm not following what you are trying to find, i.e, what would be the WHERE clause if this were a SQL statement. I think you want the fields you list (PropertyAddress, Price, etc.) for Mary Brown as client and Jack Smith as agent, but I'm not sure. Could you write a SQL statement, using pseudo code if that would make it clearer, that does what you want?
Portals are really graphical representations, not schematic objects, and may not be your friend here. A filtered portal does not filter the relationship, but only what is displayed in the portal (and it can be be pretty slow against a fair sized data set). So actions using a filtered portal may not return the results you expect.