PHP Development Environment using Docker

Since, you are asking about multi container environment, I believe you are using Docker compose for your application. To answer your question more elaborately.

1) Lets say we have three containers in docker compose, one for nginx, an fpm container for laravel and another fpm container for magento. then you docker compose file would look like. The below snippet is only an example

nginx:
  image: nginx:latest
  ports:
    - "80:80"
    - "443:443"
  links:
    - "fpmlaravel"
    - "fpmmagento"
fpmlaravel:
  image: php:latest
  volumes:
    - ./data/laravel/:/var/www/laravel
  links:
    - "nginx"
fpmmagento:
  image: php:latest
  volumes:
    - ./data/magentoroot/:/var/www/magento
  links:
    - "nginx"

The nginx vhost file for magento would be

# PHP back end
upstream backend {
    server fpmmagento:9000;
}

server {

    listen 80;
    server_name www.magento.dev magento.dev;
    root /var/www/magento;

    location ~ \.php$ {
    fastcgi_split_path_info ^(.+\.php)(/.+)$;
    fastcgi_pass backend;
    fastcgi_index index.php;
    include fastcgi_params;
    fastcgi_param  HTTPS    $fastcgi_https;
    fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
    fastcgi_param SCRIPT_NAME $fastcgi_script_name;
    fastcgi_param MAGE_RUN_TYPE $mage_type;
    fastcgi_param MAGE_RUN_CODE $mage_code;
  }
}

For fpm, make sure that fpm image is listening on port 9000.

2) Yes it is possible to have one nginx container, which routes between different fpm backends, based on nginx vhosts. But, in general it is considered a bad practice, as the main idea behind docker is to segregate your applications.