License for Pro version

I am interested in buying a license for the Pro version. The web page for that has no contact or support link, so I am posting here.

I have five sites, so a five site license fits well. However, three of the sites are on a single multisite installation. Do I buy the multisite version and, of so, will I be able to use on the non-multi-site?

Also, the non-multisite is something like xyz.org.uk and I have a development site at dev.xyz.org.uk Some licensed software allows the use on a development site with such a sub-domain prefix without counting as an extra site. What is the situation here?