Creating a Trigger in MySQL that has a JOIN

**PROBLEM:** I'm trying to create a TRIGGER that will copy records from 2 different tables (**users**, **addresses**) in database A to a single table (**users**) in database B. Basically, I'm trying to consolidate data into a single table in a different DB. I have the following TRIGGER

CREATE TRIGGER Copy db1_user to db2_users 
AFTER INSERT ON user
FOR EACH ROW 
BEGIN 
    INSERT INTO database2.users(user_id, user_email, user_firstname, user_lastname) 
        VALUES (NEW.user_id, NEW.email, NEW.first_name, NEW.last_name);
END

The above works fine, where I bend my brain is getting the other chunk of data from the address table. I've created a diagram of what I'm trying to achieve, hopefully it makes sense. Oh, it also needs to make sure that the **user_id** doesn't already exist in the target table, which it shouldn't as the **user_id** field in the source table is AUTO INCREMENT. My other question is, given the 2 source tables get written to at slightly different times, I'm not sure where to fire this TRIGGER? If I fire it on AFTER INSERT on table (users) will table (addresses) have been written to yet? Not sure - not my code (it's a WordPress application I'm drilling into), so any advice as to where to keep this TRIGGER would be great. Suggestions or assistance would be greatly appreciated.