The surprise move means the chopping and changing in the Northampton line-up is set to continue as both players are in line to make debuts against Oxford United on Saturday.
19-year-old Furlong, a right back, joins from Queens Park Rangers on a month's loan.
Centre back Brisley, 25, moves from Peterborough United for a month also as Chris Wilder seeks the winning formula against his former club.
The manager called for clarity on the future direction of the Cobblers in midweek against the backdrop of the expected supporters' protests but has been backed in the transfer market once again.