No honorific is required when addressing the former chairman of a committee.
Desmond Tutu was a Bishop, so the correct salutation would be, "Your Excellency".
the correct salutation for two men is Messrs
"Dr and Mrs Smith" is the correct salutation. (With Smith replaced with the correct surname)
committee, which
After the salutation of a business letter, the correct punctuation to use is a colon.
Dear ms
Mrs. or Ms.
madame mayor
You can, but it seems incorrect to me: you're writing to the committee as a whole, not to an individual panelist, so "Dear Panel Committee" seems better.
His Excellency, Ambassador of ................... This salutation can be used when writing to the Forein ambassadors of all countries.
chief counsel