Regarding the banner, the
tag I am assuming based on the class it has “simple-image” is a plugin you used? If so, then it probably puts that in and does not give you the flexibility to customize that. To be honest, it’s better to use a text widget and use basic HTML to load your image in that using an tag. That would solve that issue of the
being there.
For your other question… now you are really getting into more complex customization. Unless you are comfortable with CSS and Media Queries for responsive changes, you may not want to jump into that. The other issue is that this would require digging into the core files of the theme to add an extra class. What I could do on the next theme update is add this coding in which would change from say 4 widgets side by side to 2 on tablet screens and then on phones it changes to 1 widget when displayed vertically.