Let's first cover the ports:
The default FTP port is 21, not 20.
Port 66 is in the system port range (up to 1024), reserved for system purposes. Using a port above 1024 is advised.
Now to the problem:
FileZilla Server runs as a service in the Windows OS. Usually, that name is "FileZilla Server". Your second FileZilla service configuration overwrites the first one. You cannot use the installer to get two FZ Server instances onto one machine!
1. Install only the first Server with the installation program. That one will use the default name for the service.
2. Make a copy of the first installation directory, for the second instance.
3. open an Administrator command shell, navigate to the second Server's directory.
4. Refer to
https://wiki.filezilla-project.org/Comm ... 8Server%29 and use the /servicename and /servicedisplayname command line arguments to set a different service identity for the second server. Please use these two commands (not the servicenames) all lowercase, and one after the other.
5. Use the "FileZilla Server.exe" /install auto command to install the second server with the new configuration.
6. Edit the "FileZilla Server.xml" file and change the admin port.
7. Now you can start both services. Use the Admin interface to connect to the servers (you only need one but can use two for convenience). Configure them for the different ports.