I've made an awful lot of t-shirt quilts, and never worried about the logo being centered, or pieced it to center the logo. As long as the logo is in the square, that's all that matters. Nobody is going to care, trust me. I've never made one where the logo is centered in every square, and I've never had a recipient say they didn't like it.
So if one of the logo's are big - 15" and one of the others that they want to use is smaller, let's say 10" you would just piece using the back of the same tshirt - correct?