Here's the multiAdd to Cart code you'll need:
));" style="display: inline-block;background: #3da5d9 url(https://www.e-junkie.com/ej/images/newaddtocart.png) center/100px no-repeat;border: none;padding: 7px 55px;border-radius: 3px;box-shadow: 1px 2px 2px rgba(0,0,0,0.2);text-decoration:none;"> </a>
Those example URLs shown in the 2nd and 3rd lines there will need to be replaced with the actual
href= URLs from your Add to Cart button code for each item. You can add as many URLs as you want in the list, but note that all except the very last one need a comma after the closing quote at the end (as shown above).