That is correct.
It does, and is prohibited.
No, it does not. Bills of Attainder are, quite specifically, acts of the legislature.
This actually does not matter in this case: the 5th Amendment prohibits the executive from simply authorizing killings (prohibitions against the taking of life or liberty w/o due process) and the 6th explicitly states that all criminal cases have the right to a jury trial (and to mount a defense). If these killings are not the result of criminal law, then they must be civil law, and the 7th Amendment puts limitations thereon, specifically: jury-trial in any case wherein the amount in controversy exceeds $20. (And of course your life is worth more than $20.)
So, in any case these 'authorizations' of killing are utterly repugnant to the Constitution AND Murder.
Yawn.