If you're using Docker, there should be no problem running two instances of Lemmy in parallel - just make sure they're pointing at different directors for their data files, and that the docker-compose.yml files live in different folders so they get separate project names.
Not 100% sure about Ansible - you could set lemmy_base_dir in hosts/inventoty, but you might need to handle setting up and pointing at separate Postgres databases yourself.
Once you have the 2 servers running (on different ports), you'd change the config file ([Lemmy's single site example here[(https://github.com/LemmyNet/lemmy-ansible/blob/main/templates/nginx.conf)) add another server {} block, to reverse proxy to a different port depending on the domain name.