I blew the photo up large enough to see the two seams that go between the corners of the two rectangular blocks, above and below the two small center square blocks. So your first guess was right... the center two blocks are built out with a little extra strip. It won't be ugly...
What I would do first is frame all my blocks with the blue and then tackle joining them. To me it looks like the larger blocks have 2" of blue framing them, and the smaller squares all have 1" of blue around them. From there you should be able to figure out how wide the sashing pieces need to be, relative to the widths of the frames.
I believe you can do this!
