Hi
1. For add subtitle to the blog pages, there’s a known bug, the subtitle and header background field is hidden when selecting those blog templates. I will fix this issue in the next version. Now, there’s a quick solution. Just change page template to default, then you will see ‘Page Header Tagline’ field and some header related options in the common custom page setting area, add your text, change header picture, then change the template back to the blog template, save the page.
2. I’m not sure how your set up the menu, the underline is automatic added. Could I check your website?
Thanks