Answer
We cannot narrow down the situation at all.
Work Step by Step
If a person says they are a knight, they are either telling the truth as a knight or lying as a knave. When person A and B both say "I am a knight," both of them could be telling the truth, both could be lying, or either one could be telling the truth as the other lies. Thus, we cannot narrow down the possibilities as to whether persons A and B are knights or knaves.
