I manged to do the Siren one pretty easily. Used Hand cannon (Two damage upgrades) and Devils Kiss (One damage upgrade).
When you start the level, Siren is located right front of you in lower level. I just jumped down there and started spamming Hand cannon and Devils kiss. She started raising the bodies but manged to kill her before they were "alive" again. It probably would make it easier if you could get one headshot to her before anybody has noticed you.