You can embed multiple Juicebox galleries in a single post manually if you wish.

The process is as follows:
(1) Create your Juicebox galleries with the method of your choice, e.g. Lightroom plugin
(2) Upload the complete gallery folders (not just the contents) to your web server via FTP. It does not matter where you upload the folders to as long as you know where they are.
(3) Embed each gallery in your post using the baseUrl method as described here.

A few things to bear in mind:
(1) Make sure, when entering the embedding code into the body of the post, that the method of entry is 'HTML' rather than 'Visual'.
(2) You will need to embed each gallery into a <div> with a unique 'id'.
(3) In a WordPress environment, it might be easier to use absolute URLs rather than relative URLS in your embedding code in order to point to the gallery folders.
(4) When embedding multiple galleries in the same page, it is necessary to load the 'juicebox.js' file only once.

With this in mind, take the following as an example.
Say you have two gallery folders named 'gallery1' and 'gallery2' and you have uploaded them to the root of your web domain, in this example named 'www.example.com'.
Your embedding code would look something like this:

<script src="http://www.example.com/gallery1/jbcore/juicebox.js"></script>
<script>
  new juicebox({
      containerId : 'juicebox-container1',
      baseUrl : 'http://www.example.com/gallery1/',
      galleryWidth: '100%',
      galleryHeight: '600'
  });
  </script>
<div id="juicebox-container1"></div>
<script>
  new juicebox({
      containerId : 'juicebox-container2',
      baseUrl : 'http://www.example.com/gallery2/',
      galleryWidth: '100%',
      galleryHeight: '600'
  });
  </script>
<div id="juicebox-container2"></div>

Make sure you embed each new gallery into a <div> with a unique 'id'.
After embedding the first two galleries, the embedding code for the next one would look like this:

<script src="http://www.example.com/gallery3/jbcore/juicebox.js"></script>
<script>
  new juicebox({
      containerId : 'juicebox-container3',
      baseUrl : 'http://www.example.com/gallery3/',
      galleryWidth: '100%',
      galleryHeight: '600'
  });
  </script>
<div id="juicebox-container3"></div>

If you reuse 'juicebox-container' ids, then on your home page (when many posts are displayed), there will be different galleries using the same 'juicebox-container' id and problems will occur.

I imported the gallery from NextGen Gallery, after the upload is completed and when I refresh the page where the gallery has to be displayed. Only the loader appears on the center of the page, but gallery does not. Can anyone help me why this is happening?