Here you can find a fix for the elka-natalka issue.
Please tell me if it works.
This link isn't found. I'm having this similar problem, although the assassins are not attacking, just following my party around. Is Lamalha part of this group as well, or is that a hold over from NTotSC? I found her CRE file (along with Maneira, Telka, and Zeela from NTotSC) in my BWP installation, and found out that if I CLUA Lamalha into the area and talk to her, the dialog opens, and then when Lamalha turns hostile, so do Elka and Natalka. Simple work around, really if you want to initiate "honest" combat with them, I suppose....