If you pay the minstrel outside Kistandalius' shop to recite some poetry, he will come out to listen, giving you a brief opportunity to steal the random spell book from the table and dagger from the locked chest. Other than that you would have to kill him to get in the back.
I'm not sure about Commander Ralph (that room isn't very big anyway), but AFAIR you should just be able to walk into Blake's back rooms (if not, toss a teleporter stone into the back and close the door, then teleport in). You can do something similar to get into Walker's back rooms (the potion dealer): see
here and
here.
