Question: Why is Sitemap Creator creating two sitemap files? (sitemap.xml and sitemap1.xml)

Answer: If you select the “Split Sitemap” option when you save your sitemap, Sitemap Creator will generate a Sitemap Index file and one or more individual sitemap files (depending on the URL limit per sitemap file).

If only two files are generated, then you do not need to create a Sitemap Index file (so you can safely disable this option). A sitemap index is only required if there are more than 50,000 URLs in your sitemap.