Look around at other threads to get an idea for how much a 5* and 6* are worth these days.
You don't have any LE / rare 5*'s, in which case the going rate seems to be 1-2 TE depending on if they're maxed or not.
Katherine and Caym are relatively old 4*'s, so those might fetch you a TE or so from a collector. The other two, probably not so much.
Anyways, a cheap 6* - you want magic - like say Skuld will cost around 10 TE and can commonly be found for less. 10 TE will also get you Romanus, Magnus, Chiara or Orpheus (and others I'm forgetting; shopping around may find you one cheaper too, especially Romanus while everyone tries to dump her.
So the bad news is you probably can't trade what you have for a 6*, but the good news is that 10 TE is not that hard to come up with these days.