The Western family includes Parthian (Arsacid Pahlavi) and Middle Persian, while Bactrian, Sogdian, Khwarezmian, Saka, and Old Ossetic (Scytho-Sarmatian) fall under the Eastern category. The two languages of the Western group were linguistically very close to each other, but quite distinct from their eastern counterparts. On the other hand, the Eastern group was an areal entity whose languages retained some similarity to Avestan. They were inscribed in various Aramaic-derived alphabets which had ultimately evolved from the Achaemenid Imperial Aramaic script, though Bactrian was written using an adapted Greek script.
Try to answer this question if possible (otherwise reply "unanswerable"): Where did the alphabet used by Western languages come from?
unanswerable