As long as all of the clothes have been washed, it's okay to mix blends with cottons. Back when my grandmother was quilting, folks used whatever fabric was available. Just make sure they can all be washed/cleaned, the same way.
I'm with Neesie. All this fabric has been washed, and it won't make any difference anymore. If there are wools or other things, make something different from them, as the bed runner.