all your galleries are pointing to the same gallery.xml file. For multiple galleries, check the FAQ, Q16:
I'm having a similar problem, but I'm using two different simpleviewers - one as is, and one modified to load a different xml file and trigger a video player on click as opposed to changing the main image. The video player version works fine on it's own, and whichever one you go to first on the site is the same one that will load when you click on the other. Both are being loaded inside another swf. I suppose the problem could be related to how I'm unloading the swf's but i've tinkered with that functionality and haven't fixed the problem yet.
Then I assumed it had something to do with the use of singletons in sv so I tried changing the names of the classes in the modified one, but the same problem still occurs.
I see now that there's a multiple gallery fla example somewhere in the code, so i'll find that and see what insight I can gain but I've a creeping suspicion it won't make a difference.