So, I did extract using 7zip...
I am not sure if I am seeing what you made, though.
None of the files have a transparent (alpha) background, and all the colors seem wrong.
I have attached a screenshot of my file manager so you can see several of the files at once. (They all look like their previews when opened.)
I know you're being gracious to donate these in the first place, so I hate to ask you to re-upload these. But...I definitely want to use them. :) The 8-bit ones in particular. They all look so well-done..! It's just that something went weird in extraction.