If Vlad and Isabella von Carstein are in the same unit, they are inspired to fight all the harder, and gain +1 Combat Resolution. Furthermore, Vlad becomes subject to Frenzy and Hatred should Isabella be slain, and vice versa.
Source: Warhammer Armies Project: Unofficial 9th Edition (v2.2)
If Vlad and Isabella von Carstein are in the same unit, they are inspired to fight all the harder, and gain +1 Combat Resolution. Furthermore, Vlad becomes subject to Frenzy and Hatred should Isabella be slain, and vice versa.