Can't fetch property of another widget

[filvuk]

I'm trying to build a gallery page similar to the HugoBlox gallery shortcode that is editable with Decap CMS. My idea was to use a list widget, which can create a string widget (album name) and another list widget. This second list widget would create "image entries" (containing an image widget and other optional widgets). So something like this:

From here, I would've liked to set the media_folder of the image widget to a template containing the album name from the parent widget's sibling, but I cannot seem to do that, as any attempt to use templating in the media_folder property yields the error "failed to unmarshal YAML".
Is it somehow possible to fetch a widget property by name? Or is there an alternative solution I am missing? Thanks in advance.