Ahh yes, I see what you're doing.
When you set the page template to content only the sidebars still appear.
Thats down to how WordPress works.
When you set a page as a blog posts page it responds as if it was the blog posts page on the home page.
The blog post page is no longer a page as such. A page has different coding to a blog posts page and therefore cannot use a page template. A theme will generally just do whatever the home page is designed to do in that case.
So setting the page template on a page which you've set to show as a blog posts page wont work.
The pro plugin which my members have access to includes extra theme options which helps with that so you can set the home page (in your case blog page) layout separately.