are those two shirts knit t-shirts? I wouldn't applique with them--can get tricky to use. if knit, definitely use an iron on stabilizer on the back before you cut your pieces for blocks. With only 2 shirts, even with pictures added you are probably talking a lap size/wallhanging size quilt. I would suggest you alternate the picture "blocks" with a simple rail fence--putting the fabrics so that you have a gray, white, gray, blue--maybe blue (if you have enough) for borders. I would suggest you check with a local t-shirt shop to see if they will print off the pictures onto fabric for you--my local shop does a fabulous job and it's inexpensive and much better (and cheaper) than me buying special fabric, etc.