Skyrim General

[Proton]

That's pretty useful information, thanks.

I never tried killing the any other members of the Dark Brotherhood, but I had a member attack me while walking on a road before joining. I think you might be able to though since they got rid of all the rules that were in Oblivion's Dark Brotherhood. I'll test that later and see what happens.

Spoiler

When you first get contacted by the Dark Brotherhood, go to sleep and get sent to the Abandoned Shack (after waking up), killing Astrid instead of a captive will cause you to fail "With Friends Like These..." and receive the new quest, "Destroy the Dark Brotherhood!"
A mission that allows you to kill every member of the Dark Brotherhood.