How do you use a multiple leaf texture file on a sapling curve tree? Textures.com offers leaf textures in a multiple-leaf-per file format. There are also six files for all the maps.

Is the expectation that I open these in gimp and make them into separate images (somehow keeping the edits identical across all six images/maps), or is there a way to use a file like this directly in Blender where you draw bounds around the individual leaves and it assigns one of the groups randomly to each leaf instance? This is for a sapling generated tree in 2.81a.
Multiple objects can use different parts of the same material using UV mapping. In this example, The original UVs of the image plane are cut automatically when using the Knife tool. Split the edges and separate the loose parts to create multiple objects. Note the single material used.

That same material can also use the same UVs for applying alpha, normals etc...

Note: the "Import Image as Plane" is an Addon.