You have to create a JMS template rule to replicate the first slave and create the second one.
Get inspired on the tutorial video 13
www.jms2win.com/tutorial#jms12x-13
That show a similar process to replicate a "tpl_master" from the front-end.
Create a JMS template that would be
Template ID = replic_XXX
Select the template site XXX
Put a new table prefix = {site_id}_
Once you have the rules defined, you can use it to create the YYY slave site.
Site ID = yyy
Domain = yyy.com
Select the "replic_xxx" template rule.
Put the new DB name that you probably have to create before with PYPMyAdmin or other
admin tool.
Put the deploy directory /www/yyy