It will store everything locally, keep your folder structure, every metadata is inside a sidecar XML, allows for various notions of "date" and more.
Not affiliated with them, just a happy user
That's actually a fundamental requirement.
Mylio stores “Live Photos” as Photo.extension <- the “photo” it shows in the interface Photo.xmp <- all the metatdata Photo.myb <- everything else
Literally the myb is just a zip of everything else associated with the photo. So in the “Live Photo” case that would be the associated video file. If you have edited the file in Apple photos that also includes the XML Apple uses to non destructively perform the edit. As well as a copy of the original photo.
In your case you could just manually create the myb file by zipping up all the associated extra photos and changing the extension. However the interface would only show the single main photo.