Iscah: sounds like a sneeze. I understand
Jessica is derived from it, and I love
Jessica. I would not use a nickname for
Jessica.
Keziah: It's got kind of a pretty sound. You might use the nn
Kizzy. I would just use the full name.
Susannah is pretty. I like Suzannah and
Suzanne better. I guess I like
Sue best for a nn, but again, I'd rather just use the full name.