Coleraine rowers Alan Campbell and Peter Chambers both earned bronze medals at the World Cup regatta in Poznan but Richard Chambers had to be content with a fifth place.
Campbell showed a return to form as he took third in the single scull final behind Mahe Drysdale and Damir Martin.
Peter Chambers was part of the GB boat that took third in the men's lightweight four final.
Richard Chambers and Will Fletcher led the double sculls final before fading.
Chambers and Fletcher led the field at halfway but slipped back to finish nine seconds behind winners France, who finished ahead of Norway and Italy, with Irish duo Gary and Paul O'Donovan also in front of the British pair.
On Saturday, another Coleraine rower Joel Cassells and his British partner Sam Scrimgeour maintained their winning sequence this season in the non-Olympic lightweight pairs class as they told gold.
Campbell, back to full health after suffering from hay fever last month, produced a competitive performance in the single sculls final as he was less than five seconds behind New Zealander Drysdale.
London 2012 Olympic bronze medallist Campbell finished 3.36 seconds behind runner-up Croatian Martin.
Peter Chambers and his British team-mates Chris Bartley, Mark Aldred and Jono Clegg were 3.54 seconds behind winners New Zealand in the lightweight four decider with Denmark also just ahead of the GB boat.
Campbell and the Chambers brothers have been picked for the British team for the Rio Games.
The trio were medallists in London four years ago while Campbell will become the first NI competitor at four Olympic Games in Rio.