Need help with installation, got questions

Hi there,
I’m part of a very small school and got asked if I can setup jitsi on our school-server. I, totally over confident, said: yes, of course, no problem for me.
So, here I am.
My problem: our server (ubuntu server 18) has already a custom hostname because of moodle. The /etc/host looks like:
127.0.0.1 localhost
127.0.1.1 moodle
We dont have a FQDN but use a dynDNS to access the moodle-server from the internet. Something like foobar.dd-dns.de/moodle. The installation guide says I should set a domain for jitsi (which I can’t) and adjust the hostname (which I can’t either because moodle wouldn’t work then).

My question: how do I set up the server and the /etc/hosts and how to run the installation progress to get a functional jitsi without messing up the already existing moodle on the same machine? By the way: the jitsi domain should be something like foobar.dd-dns.de/jitsi

thanks, I hope you got my problem even though my bad english