Sitemaps

I have inherited a wordpress site http://www.skinewgen.com and a multisite http://www.instructorcourses.skinewgen.com

I am using the Yoast SEO plugin but there is also a BWP GSX plugin. I need to submit sitemaps for both site. They seem to be working but not fully.

First should I just be using 1 of these plugins? Do they conflict for the sitemap element?

When I use the Yoast plugin to find my xml sitemap: http://www.skinewgen.com/sitemap_index.xml i get the following error: BWP Google XML Sitemaps Error: Requested module (sitemap_index) not found or not allowed.

However if I use BWP I can find the sitemap at this address: http://www.skinewgen.com/sitemapindex.xml

With the multisite this is even more confusing as the BWP plugin can’t find the correct multisite url or http://www.instructorcourses.skinewgen.com/sitemapindex.xml but instead shows this: http://www.instructorcourses.skinewgen.com/sitemapindex_.xml (Why is the _ appearing in this url?)

Can anyone help please. It seems very messed up and as I a not from a developer background this is confusing me!

Thanks Charlie