Iceblossom

I think if you just want the block and not the sashing, it is doable in the 12" size, especially if we redraw it a bit.

It's rather clever the way the center square is made up of 4 triangles, if it was one piece and "set in" is that within your skill set or would you rather keep it the way it is? (If various people are making the blocks it is probably easier to do the way shown) I'd be making the triangles actual one piece triangles and not units that add up to a triangle.

If you divide the block into 4ths straight down the middle each way the construction would be a little different, you'd have to match the top part of the triangles onto the bases, but I think it would actually be pretty easy to put together.

Edit: So in fourths, each unit would finish at 6". You'd take a piece of blue that was 2" wide by 6.5" long. Add on a 2" white square on the end and sew through the diagonal. Then a yellow on the other side. The orange triangle would be 3" finished, for triangles you add 7/8ths instead of .5" for the seam allowance. Me, I would cut big at 4" and trim down.

Entirely doable that way at 12" but I gotta go!