2 sites, one database & one proxy. How do I set this up?

Docker Engine Compose
1

So I have to setup 2 WP sites and test SSO functionality. When I had one site I was able to use a single (& simple) compose file. But now if I try to do the same thing with 2 sites there is a conflict of ports. The easy way would be to use different ports but I would rather know how to do it correctly. Someone on stackoverflow mentioned this solution but it doesn’t work. Create a compose file that that has proxy & sql. Create another compose file in the root that will be used for the site.

version: "3.3"
  services:
    photon:
      image: "chriszarate/photon:latest"
    mysql:
     image: "mariadb:10.2"
   environment:
     MYSQL_ALLOW_EMPTY_PASSWORD: "yes"
     MYSQL_DATABASE: "wordpress"
     MYSQL_ROOT_PASSWORD: ""
 ports:
    - "3306:3306"
proxy:
  image: "jwilder/nginx-proxy:alpine"
environment:
  HSTS: "off"
  HTTPS_METHOD: "nohttps"
ports:
  - "80:80"
  - "443:443"
volumes:
  - "//var/run/docker.sock:/tmp/docker.sock:ro"
  - "./certs/self-signed:/etc/nginx/certs:ro"
  - "./conf/nginx-proxy.conf:/etc/nginx/conf.d/proxy.conf:ro"
  - "./conf/nginx-proxy-wordpress.conf:/etc/nginx/vhost.d /${DOCKER_DEV_DOMAIN}_location:ro"
networks:
 default:
   external:
     name: back

This is the one used for WordPress

version: "3.3"
services:
   wordpress:
     image: "wordpress:${WP_VERSION:-4.9.8}-php${PHP_VERSION:-7.2}-apache"
  environment:
      VIRTUAL_HOST: "${DOCKER_DEV_DOMAIN:-project.test}"
      WORDPRESS_DB_HOST: "mysql"
     WORDPRESS_DB_NAME: "wordpress"
     WORDPRESS_DB_PASSWORD: ""
    WORDPRESS_DB_USER: "root"
  depends_on:
    - "mysql"
   volumes:
     - "wp:/var/www/html:rw"
     - "./certs/ca-root/ca.crt:/tmp/certs/root.crt:ro"
     - "./conf/php-local.ini:/usr/local/etc/php/conf.d/local.ini:ro"
     - "./conf/wp-local-config.php:/usr/local/etc/php/autoprepend.php:ro"
     - "./src/vip-go-mu-plugins:/var/www/html/wp-content/mu-plugins"
     - "./src/sitename/client-mu-plugins:/var/www/html/wp-content/client-mu-plugins"
     - "./src/sitename/images:/var/www/html/wp-content/images"
     - "./src/sitename/languages:/var/www/html/wp-content/languages"
    - "./src/sitename/plugins:/var/www/html/wp-content/plugins"
    - "./src/sitename/private:/var/www/html/wp-content/private"
    - "./src/sitename/themes:/var/www/html/wp-content/themes"
    - "./src/sitename/vip-config:/var/www/html/wp-content/vip-config"
 wp-cli:
   container_name: "wp-cli"
     image: "wordpress:cli-php${PHP_VERSION:-7.2}"
   environment:
    - APACHE_RUN_USER="www-data"
    - APACHE_RUN_GROUP="www-data"
   depends_on:
     - "mysql"
   networks:
    - "back"
   volumes:
     - "wp:/var/www/html:rw"
     - "./bin/install-wp.sh:/usr/local/bin/install-wp:ro"
     - "./conf/php-local.ini:/usr/local/etc/php/conf.d/local.ini:ro"
     - "./conf/wp-local-config.php:/usr/local/etc/php/autoprepend.php:ro"
     - "./src/vip-go-mu-plugins:/var/www/html/wp-content/mu-plugins"
     - "./src/sitename/client-mu-plugins:/var/www/html/wp-content/client-mu-plugins"
     - "./src/sitename/images:/var/www/html/wp-content/images"
     - "./src/sitename/languages:/var/www/html/wp-content/languages"
     - "./src/sitename/plugins:/var/www/html/wp-content/plugins"
     - "./src/sitename/private:/var/www/html/wp-content/private"
     - "./src/sitename/themes:/var/www/html/wp-content/themes"
     - "./src/sitename/vip-config:/var/www/html/wp-content/vip-config"

networks:
  default:
    external:
      name: back
    
volumes:
  wp: {}

So what changes do I make to get this run? I am not an expert and learning as I go. So I would appreciate help in figuring this out.

TIA