I did not modify the themeswitcher script.
As my gallery serves only to show MY images, I activated the script and leave it private.
This way the script runs, but nothing shows up in the gallery.
I edited scripts of only three files ... album.php, image.php and index.php
The codes to run zenphoto is the same for both themes.
I am using the basic theme as a template for the gallery, but I created a css (gallery.css that I inserted <link rel="stylesheet" right after the basic css file) to customize and overwrite some values of the basic/styles/light.css
I edited files in my websites to point to its proper theme by adding [?themeSwitcher=site1] at the end of all links.
As I am using Google AdSense and Analytics, it is important to use the google code of the main site IN ALL THEMES.
Because when you are accessing the gallery, in fact, you are leaving the original site.
For sitemaps, I am using xml-sitemaps.com to point to my main site and the /gallery/ folder.
For the other websites, I only create sitemap for the site, as there are no more /gallery/ in the site folder.
Everything looks great!