Adjust banner image size+location when on mobile

Site URL: https://www.nicolemarkwick.com

Hi folks, 
Does anyone know how to: 
1) Customize the way a parallax banner background image appears on mobile (narrow screens)? Specifically, I'd like to be able to "zoom" in on a background image a certain % and set the position/location of it on the screen when in mobile. 
2) Add a transparent overlay to a banner only on mobile, so that text on top is clearer? 
3) Is there a way to make a parallax banner invisible on mobile? 

Some specific examples below: 

The banners look neat on desktop but look pretty horrible on mobile! I'd like to use the left half of the first background so it's all photo (then figure out how to make "What clients say" have a while background....next steps!) and get rid of the background completely on the second image.

Thanks a million! 

Do you still need help on this?

I found some other problems.

Site URL: https://www.nicolemarkwick.com/

1. (Tablet – Homepage) “Meaningful change through co-design”, texts are cut off

2. (Tablet – Homepage) Equal height all boxes?

3. (Tablet/Mobile – About) Image doesn’t show in full size

4. (Tablet – Contact/Services) On tablet. texts disappear and layout doesn’t look good.

https://www.nicolemarkwick.com/contact

(Desktop)

(Tablet)             

5. (Mobile – Contact)

6. (Tablet – Portfolio) Right and left margin have a big gap make content is a bit narrow. Do you want increase content width?

https://www.nicolemarkwick.com/portfolio

7. (Tablet – Homepage) “implementation” in box 3 don’t lie on the same row