I want this, but is a Tiled editor friendly format available?
No. It was created for the use with RPGMaker, so you'd probably have to edit the sheets yourself to make them work with Tiled. (I'm not familiar with how the layout would need to be, but I guess the autotiles would not work as they are setup now.)
I bought the tileset, and I want to know if I have permission to edit/redraw the tiles as I see fit.
Also, I'd like to know if sharing between artists whom I commission is allowed.
Edits are allowed for usage within your project. You aren't allowed to share or sell the edited assets.
I'm ok with you handing the files to a commissioned artist for them to work with those files. They aren't allowed to use the art assets (original or edited) on their own project (they'd need to buy their own license for that) and are not allowed to sell the edits they made as an asset pack, to other clients, or in whichever other way. ;3
Do you plan to make more tilesets in this styl?