How can Borden let his brother die? Angier at least was killing duplicates created by the machine, but they were normal born humans and he just let his brother be arrested and killed!

It also doesn't make sense Cutter joining with Borden. Borden was letting his own brother die, that's worse than Angier making a trick to get Borden convicted of morder!

And how could Angier drown 100 dupes and even keep them and nobody even Cutter figure it? I understand the workers were blind and wouldn't see it happening, but of course they'd hear the water and somebody falling on it.