Parthian Problems

I think there are some problems with the profiles of the Parthian Kings. Just as an example:

Artabanus IV, king of Parthia and Media

his profile shows him as Arsaces XXVIII Vologaeses IV son of Vologaeses IV and brother of Artabanus. I think that is not accurate.

In addition, the wikipedia list of Parthian Kings conflicts with the naming in the Encyclopaedia Britanica for many of the Parthian Kings. For example, wikipedia lists lists as Volageses V the person that Britanica describes as IV.

In looking through the Parthian Kings this example seems to be fairly typical of the issues. Anyone have any ideas on resolving these?