Trying to install php5.6 alongside 7.x that comes with Virtualmin/Webmin

So I'm really new to VPS. And domain hosting. But this seems to be the right place to ask newbie questions.

I've just spun up a Ubuntu 16.04 install on a VPS. I chose Ubuntu because I use it at work, and I hadn't seen anything saying this was a bad idea.

I see that PHP 7.x is installed along with Virtualmin. But I would like to install a full php5.6 (or whatever the highest php5.x version is) package to have the option to run if I need to. In various places I found reference to commands like this:

apt install php5.6 php5.6-cgi php5.6-mysql

or

apt-get install php5.6-mysql php5.6-curl php5.6-gd php-pear php-imagick php5.6-imap php5.6-mcrypt php-memcache php5.6-tidy php5.6-xmlrpc php5.6-xsl php5.6-mbstring php5.6-zip php5.6-fpm php5.6-cgi php5.6-cli

or

add-apt-repository ppa:ondrej/php apt-get install php5.6-mysql php5.6-curl php5.6-gd php-pear php-imagick php5.6-imap php5.6-mcrypt php-memcache php5.6-tidy php5.6-xmlrpc php5.6-xsl php5.6-mbstring php5.6-zip php5.6-fpm php5.6-cgi php5.6-cli

But none of these work. They alll produce output like this:

Reading package lists... Done Building dependency tree Reading state information... Done E: Unable to locate package php5.6-mysql E: Couldn't find any package by glob 'php5.6-mysql' E: Couldn't find any package by regex 'php5.6-mysql' E: Unable to locate package php5.6-curl E: Couldn't find any package by glob 'php5.6-curl' E: Couldn't find any package by regex 'php5.6-curl' E: Unable to locate package php5.6-gd E: Couldn't find any package by glob 'php5.6-gd' E: Couldn't find any package by regex 'php5.6-gd' E: Unable to locate package php5.6-imap E: Couldn't find any package by glob 'php5.6-imap' E: Couldn't find any package by regex 'php5.6-imap' E: Unable to locate package php5.6-mcrypt E: Couldn't find any package by glob 'php5.6-mcrypt' E: Couldn't find any package by regex 'php5.6-mcrypt' E: Unable to locate package php5.6-tidy E: Couldn't find any package by glob 'php5.6-tidy' E: Couldn't find any package by regex 'php5.6-tidy' E: Unable to locate package php5.6-xmlrpc E: Couldn't find any package by glob 'php5.6-xmlrpc' E: Couldn't find any package by regex 'php5.6-xmlrpc' E: Unable to locate package php5.6-xsl E: Couldn't find any package by glob 'php5.6-xsl' E: Couldn't find any package by regex 'php5.6-xsl' E: Unable to locate package php5.6-mbstring E: Couldn't find any package by glob 'php5.6-mbstring' E: Couldn't find any package by regex 'php5.6-mbstring' E: Unable to locate package php5.6-zip E: Couldn't find any package by glob 'php5.6-zip' E: Couldn't find any package by regex 'php5.6-zip' E: Unable to locate package php5.6-fpm E: Couldn't find any package by glob 'php5.6-fpm' E: Couldn't find any package by regex 'php5.6-fpm' E: Unable to locate package php5.6-cgi E: Couldn't find any package by glob 'php5.6-cgi' E: Couldn't find any package by regex 'php5.6-cgi' E: Unable to locate package php5.6-cli E: Couldn't find any package by glob 'php5.6-cli' E: Couldn't find any package by regex 'php5.6-cli'

I'm glad to be pointed at appropriate webpages to find the commands myself...

Thanks, Norman