The Shias who hold belief of kufr are: who regard the companions as kafir, who blame on Hazrat Ayshah (Razi Allahu anha) of adultery or who believe that Hazrat Gebriel (the angle) mistakenly put revelation to Prophet Muhammad (Sallallahu Alaihi Wasallam), so such Shias are kafir, it is unlawful to marry with them.
The Shias are not ahl kitab, though the Jews are ahl kitab, but today’s Jews are atheists, they no longer remained ahl kitab in the sense that their women are lawful for Muslims to marry. For detail, please see Maariful Quran vol 2, by Mufti Muhammad Shafi RA.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband