Your virtualhost without servername directive (you have it commented) means all request will go to that virtualhost, making /opt/librenms/html the root directory for all.
You have 2 options:
A) Fully move to virtual host domains
That means having a sub domain for each one, then configure a virtualhost for each with different ServerName directive (librenms.yourdomain, wp.yourdomain, zp.yourdomain,etc…)
B) Set the documentroot directive to /var/www then make a symbolic link from /var/www/librenms to /opt/librenms/html (never used this one so not really sure if you have to do anything else)