How do I manage conflicts like this when using save folders on GitHub?

We have a team working on a project and we have the same issue over and over again. Imagine that we have 3 sprites, all named S1, S2, S3. Zack adds a S4 sprite on layout 1, and Bill adds a S5 sprite on layout 2, before receiving the changes made by the Zack.

Zack's project.c3proj file stays like this:

"S1",

"S2",

"S3",

"S4"

While Bill's project.c3proj file stays like this:

"S1",

"S2",

"S3",

"S5"

Then, when uploading both versions, we get the error, and we need to choose which version we keep. Is there any way to keep both and merge both S4 and S5, in separate lines?