Real Estate listing

I am rebuilding a commercial real estate's website (very early). Eventually I will need to have a property listing page. They use a system called Astro Applications, which organizes their listings, and has tools to help clients display their properties. The problem I am having is getting what I need. Astro said they haven't heard of Squarespace, and only did templates for Wordpress before. He handed off to me a few .php files (he called it documentation), and said he could send over the XML calls the current website is using. I had no idea what to do with them. He also mentioned something about the API key, but I wasn't sure if that was right. Does anyone know what I need to bring these listings from their current site to the new one? 
Here are the php files he sent to me.

This looks like complex.

It looks like you will need to hire a coder to help you with this.