Hi @fran.sarlija,
I may have a basic solution for the sort of thing you’re looking for here!
I believe this comes down to making sure that everything is kept separate, as you have done here. For example, I had a go at an implementation like this using two target images. When ‘found’, one shows an <a-box> and the other an <a-sphere>.
In the index.html, I start this process by adding both of my target images to the assets library:
<a-assets>
<a-asset-item id="target-file-one" src="example-tracking-image.zpt"/>
<a-asset-item id="target-file-two" src="targetImage_01.zpt"/>
</a-assets>
I’ve made sure to give my a-asset-item target file and image-group different ids, and to include them as such.
<!-- Target File One -->
<a-entity zappar-image="target: #target-file-one" id="image-group-one">
<!-- PLACE 3D OBJECTS HERE TO TRACK FROM THE CENTER OF THE IMAGE -->
<a-box position="0 0 0.5"></a-box>
</a-entity>
<!-- Target File Two -->
<a-entity zappar-image="target: #target-file-two" id="image-group-two">
<!-- PLACE 3D OBJECTS HERE TO TRACK FROM THE CENTER OF THE IMAGE -->
<a-sphere position="0 0 0.5"></a-sphere>
</a-entity>
From here, our script should be pretty straightforward. Because we have made two separate targets, we can target them as such without effecting each other. So for example, in index.js:
let ImageGroupOne = document.getElementById("image-group-one");
let ImageGroupTwo = document.getElementById("image-group-two");
let imageOneVisible = false;
let imageTwoVisible = false;
We can then separately use the same event listeners, making sure to use the correct variables:
ImageGroupOne.addEventListener("zappar-visible", () => {
// The image has appeared so show the group
ImageGroupOne.setAttribute("visible", "true");
imageOneVisible = true;
});
ImageGroupTwo.addEventListener("zappar-visible", () => {
// The image has appeared so show the group
ImageGroupTwo.setAttribute("visible", "true");
imageTwoVisible = true;
});
You could then do the same thing for the zappar-notvisible event.
Hopefully that makes sense! The example I worked on uses webpack, but it should be translatable for standalone builds too! 
Have a great day!
Francesca 
