I have made many t-shirt quilts. I find using fusiable web as a stabalizer keeps them straight when cutting. My DH cut a 12"&14" square out of clear plexiaglass. I marked the center and I line up my t-shirts in the middle. This gives me the best idea of how it will look on the quilt. 14" seems better for larger t-shirts. Children I use 12" or smaller. I use corner stones and sashing between . I then knot them,but I knot them and tie them from underneath. That way the strings are underneath and doesn't distort the design. It is a little more work ,but I perfer to do mine this way. I agree most shops do not like to quilt them and usually won't say how they will turn out. Don't give up making them . People usually just want the memories recorded the best way you know how. Do your best workmanship and it will be rewarding