1. If by "combine" you mean share a user database, then yes you could do this with a
WordPress multisite setup. Both theme cannot be used on a single installation at the same time though, as they require their own instance of WordPress to be installed.
2. Yes we definitely recommend the use of a child theme when
customizing any of our themes. When you carry out an update, all theme files are essentially replaced so using a child theme is the most effective way of ensuring you don't lose all of your changes when you upgrade.
3. Our themes are not designed to use the static homepage option by default as certain links and functions will not work correctly. You'd need to make some theme modifications in order to make those work correctly. Another way outside of this would be if you had a different theme for the homepage, and installed the others in subdirectories, you could have a different homepage altogether. Thanks.
