I didn't mind Icheb and Mezoti, but the twins Rebi and Azan were absolutely pointless. I don't think they said 10 words between them and had no character whatsoever. I can't tell if the kids were decent actors or not since they were given squat to do. They should have retooled "Imperfection" by having one twin save the other by sacrificing his cortical node. Would have had the audience care for them at least a little.
I think it makes sense they didn't speak. Borg are slaves, a slave that speaks or speaks out of term is ususally beaten & tortured and made an example of. As young children the affects of Borg slavery will say with them for years, the effect is them being used to having others speak for them.
Much like Hugh, a good slave keeps it's mouth shut, it's head down and does it's work. Speaking up gets you noticed and deactivated.