If masonry grid with all 3 galleries is necessary, then you will probably have to change the database structure 
- Create separate collections for the gallery, where will be all images.
- Each item in this collection should have
- image field
- reference field to artists collection
- gallery type
It will be a bit more complicated and may hit the Webflow CMS limits (maximum number of items in the collection) if site doesn’t have a paid CMS hosting