Now that I'm thoroughly confused...

You can point another domain to a directory in your account (right, Admin?)

This would basically be another set of files in that directory.

If you want both domains to point to the exact same content, then they would both point to your public_html.

If you want to create a subdomain, the easiest way is to create a directory that has the 1st level name of the subdomain.  In your case, a directory called smithfamily.

Then create a subdomain smithfamily.jonesfamily.com, and it will automatically point to the directory of that name.

As far as more than one domain, just send an email to support@lunarpages.com and they'll answer any questions you have as far as pricing.