When configuration php-fpm you are able to configure it using ports or sockets.
The best thing to do is configure with socks as this avoids the networking stack associated with ports.
This means that php-fpm will be using files (sockets) to run which could be considered slower because of potential slow HDDs however the files are mostly stored in RAM so it makes accessing them significantly quicker.

To specify different server pools for each website you can create a website pool in the /etc/php-fpm.d/ directory.
E.g /etc/php-fpm.d/lukeslinux.co.uk
You would then want something similar to the following:

[lukeslinux.co.uk]

listen = /run/php-fpm/lukeslinux.co.uk.sock
listen.allowed_clients = 127.0.0.1

user = nginx
group = nginx

pm = dynamic
pm.max_children = 50
pm.start_servers = 5
pm.min_spare_servers = 5
pm.max_spare_servers = 35

slowlog = /var/log/php-fpm/lukeslinux.co.uk-slow.log

php_admin_value[error_log] = /var/log/php-fpm/lukeslinux.co.uk-error.log
php_admin_flag[log_errors] = on

php_value[session.save_handler] = files
php_value[session.save_path] = /var/lib/php/session

grep "pm.max_spare_servers" /etc/php-fpm.d/www.conf

ps -eo cmd,pid,pcpu --sort:-pcpu | grep -v grep | grep -c php-fpm