I would use the two small one in the center with a narrow sashing, join them into one block. You might even incoporate some pictures of your daughter wearing some of the T-Shirts. As for the blocks, just add sashing to make your blocks the same size. I too am going to make a T-Shirt quilt of all my Betty Boop shirts, hopefully soon.
straw.com/quilting/articles/teequilts.html has an article on how to place /make a T-Shirt quilt.