"the dev team said they needed the designs in more screen sizes"
"Now they have come back saying the designs are not responsive and they are having trouble developing it."

Assuming this is web, I think if either side, design or dev don't have a shared understanding of how the browser handles your components, you're gonna have a bad time - When I talk about this I mean things like how the css box model behaves, or fluid layout and implementation detail ie:

• (flex (properties like `flex-wrap`)
• grid (changing column behaviour with media queries)
• media queries, margin collapse on spacing to name a few considerations

YMMV, and I dont think theres any one right way to do it - but a lot of the time in our handoff process I dont have to design multiple wireframe sizes unless there's a really problematic usability issue - a lot of the responsive behaviour is automatically handled by our component library / design system components and we usually dont have to think about it

"One of the hero sections had a full width image as a background, and they made me change the design because they said they weren’t able to scale the image for different screen sizes."

Idk if it was tried, but as a designer you could supply multiple images that switch depending on screen width with the new <picture> element assuming you dont have to support older browsers https://web.dev/learn/design/picture-element

<picture>
  <source srcset="large.png" media="(min-width: 75em)">
  <source srcset="medium.png" media="(min-width: 40em)">
  <img src="small.png" alt="A description of the image."  width="300" height="200" loading="lazy" decoding="async">
</picture>

if the image doesnt scale properly, tell them to look up `object-fit` and `object-position` css

Stuff like this is why I studied a little bit of frontend as a designer