I think I've got a somewhat uncommon issue. My wordpress site uses a custom theme, but I wanted to add a blog alongside that, without using multisite because my host charges 3x the amount for such a feature.
What I found was the ability to override an individual page's theme using a plugin, called Page Theme (Click for theme home page).
This worked great - until I tried to load posts of a specific category. I have a new category with slug blog-posts, cat=14, which are the only ones I want to show up on the page.
I set my site's default theme back to my Custom Theme, then overrode the Blog page to be the twentytwelve theme. I then set the page template to a php file that queries for my blog posts (following instructions similar to these)
However, all of the formatting is lost.
If I go to my site's settings, Reading > Static Page > and then select the Blog page for Posts, the formatting is back, but its showing EVERY post.
I realized the templates I can select, because I have my Custom Theme set to default, are only those in my /themes/CustomTheme/.. folder. I also learned that when you select the static posts page, it will look up the index.php for that theme (in this case, twentytwelves index, which looks great!)... But I'm not sure how to QUERY for the posts I would like, while maintaining the TwentyTwelve theme format.
Any guidance is very much appreciated. 4 hours spent on this and I'm just where I started :(