sir or madam
You could write either, Yours Sincerely (if you know them) or Yours Faithfully (if you don't know them).
Comparative: more faithfully Superlative: most faithfully
Yours Faithfully
Faithfully is an adverb and does not have a plural form. There cannot be more than one faithfully.
The servant stayed faithfully by his master, no matter the problem. The novel was translated as faithfully as possible.
You thank whoever you are sending the letter to the on the right side of the paper you write Yours faithfully, your signature, your name.
Dear Sir/Madam, My brother is staying with me presently at the above address Yours faithfully
faithfully
I am faithfully yours.
Comparative - more reliable Superlative - most reliable.
Dependably and reliably are synonyms for faithfully.
My sister Faithfully prayed to god