Thanks - I will look into the two pickers.

I still also would like to know how to retrieve data in my own custom property editor. The XML data is already saved on the node before I will try to retrieve it.

Thanks - that sent me in the right direction:

App_Plugins\MartinRud.XmlPicker\picker.controller.js

angular.module("umbraco").controller("ImagePickerPluginController", function ($scope, editorState, contentResource) {
    console.log(editorState.current.variants[0].tabs);

    var hrPhotosAlias = "hr_photos";
    var primaryImageAlias = "primaryImage";

    // Find the indices of properties
    var hrPhotosIndex = -1;
    var primaryImageIndex = -1;

    for (var i = 0; i < editorState.current.variants[0].tabs[0].properties.length; i++) {
        var property = editorState.current.variants[0].tabs[0].properties[i];
        if (property.alias === hrPhotosAlias) {
            hrPhotosIndex = i;
        } else if (property.alias === primaryImageAlias) {
            primaryImageIndex = i;
        }

        // Exit the loop early if both properties are found
        if (hrPhotosIndex !== -1 && primaryImageIndex !== -1) {
            break;
        }
    }
    console.log(hrPhotosIndex, primaryImageIndex)
    if (hrPhotosIndex !== -1 && primaryImageIndex !== -1) {
        // Get the property value by alias
        var hrPhotosXml = editorState.current.variants[0].tabs[0].properties[hrPhotosIndex].value;

        // Create an empty array to store the image data
        $scope.imageOptions = [];

        // Parse the XML data
        var parser = new DOMParser();
        var xmlDoc = parser.parseFromString(hrPhotosXml, "text/xml");
        var photoNodes = xmlDoc.getElementsByTagName("photo");

        // Loop through the <photo> elements and add them as options
        for (var j = 0; j < photoNodes.length; j++) {
            var photo = photoNodes[j];
            var url = photo.querySelector("url").textContent;
            var descuk = photo.querySelector("descuk").textContent;

            var filename = url.substring(url.lastIndexOf('/') + 1);
            var label = descuk + " (" + filename + ")";

            $scope.imageOptions.push({ value: url, label: label });
        }


        //$scope.selectedImage = hrPhotosXml;
        $scope.$watch("selectedImage", function (newValue, oldValue) {
            editorState.current.variants[0].tabs[0].properties[primaryImageIndex].value = newValue;
        });
    }
});

App_Plugins\MartinRud.XmlPicker\picker.html

<div class="image-picker" ng-controller="ImagePickerPluginController">
    <select ng-model="selectedImage"
        ng-options="image.value as image.label for image in imageOptions | orderBy:'label'">
        <option value="">Select an image</option>
    </select>
</div>

But how do I save the choice when editor hits Save og Publish?

Right now I transfer the chosen value to another property ("primaryImageAlias" of type textstring). Ideally I would like the choice to be saved to the property itself, but that's not important now.