It's spelled "Voivode" not "voivod"
In English, "voivod" is an accepted -- albeit rare -- alternate spelling of "voivode." The word has a number of English spellings; merriam-webster.com lists "voivode" itself as an alternate spelling of "vaivode," which I've never seen before.
Since a web search shows the most common use of "voivod" as the name of a Canadian metal band, I think I'll eschew it in favor of "voivode."
titles are capitalized
You're correct in this instance. I had a brain stone and it didn't register that putting the title in apposition to the name of a people was, in fact, creating a well-formed personal title. So he is more properly the Voivode of the Karaschin Clan.
But "titles are capitalized" is not a good rule of thumb. Voivode Tomaj is a voivode, not a Voivode.