Complex sentence: Those titles were largely nominal though since all three thrones were already occupated by others, respectively Artavasdes II of Armenia, Artavasdes I of Media and Phraates IV of Parthia.
Split into simpler sentences: Those titles were largely nominal though since all three thrones were already occupated by others. Respectively Artavasdes II of Armenia, Artavasdes I of Media and Phraates IV of Parthia.