Multiple JOIN of 6 tables via 5 database instances

I’m currently reengineering my corporates user management and created a table which lists all users of all the 5 database instances. Next step is, that I need to write a query which shows me all the roles of a user which he has of all instances.

I already used UNION ALL, but the output was unstructured and you couldn’t tell which role on which instance. So I tried the following for only 3 tables:

SELECT W.GRANTED_ROLE "GRANTED_ROLE_DB1", V.GRANTED_ROLE "GRANTED_ROLE_DB2"
FROM SCHEMA.USR_ALL_USERS U
LEFT OUTER JOIN SYS.DBA_ROLE_PRIVS W
   ON (U.USERNAME = W.GRANTEE AND U.DB_INSTANCE = 'DB1')
LEFT OUTER JOIN SYS.DBA_ROLE_PRIVS@DB2_LINK V
   ON (U.USERNAME = V.GRANTEE AND U.DB_INSTANCE = 'DB2')
WHERE U.USERNAME = 'USER'
ORDER BY U.USERNAME ASC;

It actually worked, but the output wasn’t satisfying:

GRANTED_ROLE_DB1            GRANTED_ROLE_DB2
--------------------------- --------------------------
ROLE_1
ROLE_2
ROLE_3
ROLE_4
                            ROLE_1
                            ROLE_2
                            ROLE_4
                            ROLE_5
                            ROLE_6

Is there any way to make an output like this:

GRANTED_ROLE_DB1            GRANTED_ROLE_DB2
--------------------------- --------------------------
ROLE_1                      ROLE_1
ROLE_2                      ROLE_2
ROLE_3
ROLE_4                      ROLE_4
                            ROLE_5
                            ROLE_6

I tried ON ((U.USERNAME = V.GRANTEE OR W.GRANTED_ROLE = V.GRANTED_ROLE) AND U.DB_INSTANCE = 'DB2') but the output was even worse.

You guys have any suggestions or helpful thoughts?