Yes you can add the extra 1/4 to the 4 middle strips which is one way
...I always cut my outside pieces larger abt 1/2 inch over on the outside all around until sq'd up.
This way when you sq up each block you'll have slightly larger block that you can then cut to your exact size. You'd have the exact 1/4 inch your missing then. As you can see on the bottom right once you sew that to another block or sashing your going to lose your point. At least that's how it looks in the photo you don't have 1/4 inch seam on that one...
So when you sq each of those 4 blocks each should be 6 1/2 sq and when you sew them together will measure 12 1/2.
Regarding getting a certain subject in a section...again you have to cut pieces larger center the subject and you'll have the extra fabric to trim away to the 1/4 inch if it's a center piece...If an outside piece just remember to leave more then the 1/4 until sq'ing up. Hope this makes sense and helps...