Duffy, 19, has been a permanent fixture in the Wolves under 20s this season having made 13 appearances out of a possible 14, scoring one try.
Prop forward Brennan, 19, can also play in the back row and has made eight appearances in the under 20s having progressed from the under 18s set-up.
A club statement read: “This opportunity will enable them to gain experience and build up some game-time at Championship 1 level. Barrow will also benefit greatly as the pair will help boost their squad and provide much needed cover.
“All at the club would like to wish Ryan and Bradley the best of luck for their time with Barrow.”
The pair will join team mate Ryan Shaw, who is also on a dual-registration deal at Craven Park.