Michael Ciancaglini/Joey Ciancaglini
IMO, I don't think this can be topped!
I don't know about that; I think Quiet Dom not saving his son from death may be more disturbing to me. But yea, A brother murdering another brother is horrid.
Let's also not forget, Steve Maggaddino kidnapping his cousin Joe Bonanno. It's been said that this was a faked kidnapping, however.