I've been looking for guidance on whether a SAR is required for instances of fraud where the activity is <$25,000 and where the victim of the fraud refuses to file either a police report or affidavit of fraud against their family member.

Your decision should not be based on the filing of a police report or affidavit of fraud by any party. Filing is based simply on the bank's knowledge of any transaction, or series of transactions, occurring or attempted through your institution that hits the trigger amount.