If you haven't already:

Include the code in a weekly job, reconfigure Sql Server logs and select an appropriate number like say 20.

Now you will cycle error log every week and...

1. List the users in the database.

Use Database

SELECT name, type_desc FROM sys.database_principals

Filter out what ever you need like

where type_desc = 'sql_user'

OR type_desc = 'windows_user'

2. List the logins and passwords.

Create the...

Check your database for deny.

USE [DATABASE]

SELECT user_name([memberuid]) as [Username], User_Name([groupuid]) as [Role_Name]

FROM [sys].[sysmembers]

where User_Name([groupuid]) = 'db_denydatareader'

Something with the public role?

Check if you accidently checked db_denydatawriter for the login.

One option is to configure the two instances with their own IP addresses and then you can use port 1433 on both.

This way you can use DNS for all your...