Oksana growls at Vlad, and he stalks her and I've realized I've got to keep them apart when I'm not home. My vet even suggested giving Vlad Prozac, like I did with Czari when I was trying to get her assimilated into the group.
I have to say, I don't want to jinx things, but so far the daily separation seems to be working. I've kept Oksana and Vlad apart while at work and let her out of the bathroom when I get home. Vlad has left her alone.
I think using some flower essences might benefit Ziggy and Zuzu too. I'm going to try them myself. It can't hurt.