We don't have synonyms for affiants yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are affiance, affiant and fiants.
(n) :
(originally US, now Canada, US, law) An individual witness whose statement is contained in an affidavit; (generally) an individual who makes a sworn deposition; a deponent.
(n) :
(originally US, now Canada, US, law) An individual witness whose statement is contained in an affidavit; (generally) an individual who makes a sworn deposition; a deponent.