How do I say “the other person”?

Question

I want to write a small dialogue. How do I say "the other person says/answers etc."?

Then, one said...and the other replied...

When names are available I usually use those to indicate who says what, but when there are no names available, what do you do?

Answer 1

How do I say "the other person says/answers etc."?

もう一人の人が 言い/答え ました is the common way of saying it.
In polite language it should be もう一人の方{かた}が おっしゃいました／言われました etc.