Thanks, good catch. I just added an extra sheet to the add-on file (tileA1_fallb in addition to the existing sheet) with the brown/orange grass color. If you redownload the fourseasons update it should be included now.
As for the tileset, the side parts are actually in the middle of the corner pieces (the way RM works is it uses 8x8 half-tiles). Here's a visual to show you what I mean:
I believe that you can set up the tileset in Godot to use 8x8 tiles for the water layer, or alternatively shift the tileset by 8 pixels to pull the side piece.
Hope that makes sense. Thanks!