You can't apply a sprite to a quad, but you could set it up in Blender to work better. So, you have a hierarchy set up in blender - set it up as an armature. You can then delete the one geometry node after it gets into Unity, or just not export it. You can then set up the sprites on each bone, or attach them to the bone.
Sounds like the easiest way to go about this. Its not that straightforward initially, but all of this can be automated later on.