Who praises Macbeth's castle

In Shakespeare's time martin was a slang term for a person who is easily deceived. However, while Banquo realizes that Macbeth's home is hardly congenial, there is situation irony present in his remark, as well.

Explanation:

In Act I, Scene 6 of "Macbeth," King Duncan, the Scottish lords, and their attendants arrive outside Macbeth's castle.  With great situational irony, King Duncan praises the congenial atmosphere and pleasant environment, thanking Lady Macbeth for her hospitality:

This castle hath a pleasant seat; the air/Nimbly and sweetly recommends itself/Unto our gentle senses. (I,vi,1-3)

Explanation:

about the letter or who wrote the letter

there is no short story here so that i can answer the question.