Carlin won the 400m freestyle in four minutes 5.69 seconds, ahead of British team-mate Camilla Hattersley.
Stephen Milne won 1500m freestyle gold in 15:12.33, with Tim Shuttleworth taking bronze in 15:16.09.
Peaty raced to 50m breaststroke victory in 26.68 seconds, while James Guy claimed the 200m freestyle in 1:46.91.
Find out how to get into swimming with our special guide.
British athletes completed a clean sweep of the medals in the women's 50m backstroke, with Georgia Davies winning in 27.84 seconds from Fran Halsall (27.92) and Jess Fullalove (28.55).
Chloe Tutton won silver in the women's 100m breaststroke, while Ben Proud won silver in the 50m freestyle.
There were bronze medals for Max Litchfield in the 400m individual medley, Chris Walker-Hebborn in the 100m backstroke and Ross Murdoch in the 200m breaststroke.
Sign up to My Sport to follow swimming news and reports on the BBC app.
Jazz Carlin and Adam Peaty were among the winners on the final day of the Mare Nostrum meet in Barcelona as Britain collected 14 medals.