It's quite complicated...
You have to write a javascript gallery script of some sort that would allow you have multiple Slideshows on the page.
It would be easier as a plugin. You would insert the plugin into your textarea and tell it which exhibit (set of images) to grab. You woudln't be able to grab from just one exhibit - there is no way to distinguish things going that route.
It would be so much easier to have just one Slideshow and simply separate things with title and caption - use text to distinguish whatever it is you think having two separate ones are going to achieve.
Slideshow is a terrible format - I've never liked this format even if it was/is popular - because is has that jaggedness from one image to the next. With two Slideshows I can imagine just how much worse that's going to be...
Slideshow would work better if people chose images of the same size and orientation - but they never do (and there are good reasons for that).
I've been working on a new slideshow I'm calling Slides. I've resolved the jaggedness by only allowing the slides on the exhibit to be on display - the body text is hidden when viewed. It functions via the Visual Index format - begins with thumbnails.