Responsive iFrame

The client wish is to display roundabout 30 Kitchens, that are sold in a portal called https://www.kleinanzeigen.de. One solution to integrate this listing in the current website is to display a gallery of portfolios and there realize it with an iFrame. Another: solve it with a plugin or something similar.

1) How is it possible to integrate a responsive iFrame without issues – I didn´t succeed with the following code – it crashes the website complete?
2) And the other problem is that browsers doesn´t allow the display of iFrames. How to solve this?
3) Or is it possible to integrate directly the adverts via plugin/other solution?

IFRAME EXAMPLE

<div class="container"><iframe class="responsive-iframe" src="https://www.kleinanzeigen.de/s-anzeige/moderne-doppelhaushaelfte-mit-keller-in-ruhiger-lage-kueche-geschenkt-/3077951470-208-6482"></iframe></div>

CSS

/***** RESPONSIVE IFRAME *****/ 
.container {
  position: relative;
  overflow: hidden;
  width: 100%;
  padding-top: 56.25%; /* 16:9 Aspect Ratio (divide 9 by 16 = 0.5625) */
}

/* Then style the iframe to fit in the container div with full height and width */
.responsive-iframe {
  position: absolute;
  top: 0;
  left: 0;
  bottom: 0;
  right: 0;
  width: 100%;
  height: 100%;
}