Yes, that would require to have multiple WordPress instances on the same database. If you want to use WordPress multi user you can use this:
Install your primary blog as normal, and set your CUSTOM_USER keys in your wp-config:
Create the wp-config.php for your second blog, using the same DB Connection information.
You also need to set AUTH_KEY, SECURE_AUTH_KEY, LOGGED_IN_KEY, NONCE_KEY, and the CUSTOM_USER keys to the same value as the first. You will also need to set $table_prefix to a unique value.
Install the second blog and instead of getting a random password for the admin user, it should tell you that it found the user and is using that password.
Repeat steps 2 and 3 until all blogs are successfully installed.