Doctor Who Fluxx - do Dalek cards affect all doctors
The text on the Dalek creeper is not exactly clear: "if the Doctor is anywhere on the table, during your turn you can discard both him and this". But all doctors are "the doctor" (The third doctor, the nineth doctor etc..) so you can safely assume this counts for a single "the doctor" card.

If you look at the the FAQ:


  Q: Can I trash someone else’s Doctor to get rid of my Dalek, instead
  of my own?
  
  A: The Dalek says you can discard the Doctor from anywhere on the
  table. You’re not required to kill your own Doctor first, so, it makes
  the most sense, strategically, for your Dalek to target someone else’s
  Doctor.


There is no indication that you can discard both. It just discards one instance of "the Doctor". It is up to you to decide Who.