It is well known that the Rāfiḍa or the Shīʿa slander many of the companions, regard them disbelievers and have many groups amongst them. So are they all considered disbelievers or do they require detail explanation (for their kufr) and what is the ruling on their [food] sacrifices?

Shaykh Ṣāliḥ al-Fawzān:

In any case, those who slander the Companions and do not make innocent ʿĀʾisha from that which Allāh ﷻ has freed her from of accusations, those are disbelievers. So do not eat their sacrifices. Secondly, the majority of Ṣūfīs now have become grave-worshippers. They worship graves, build shrines over them, seek aid and supplicate to other than Allāh ﷻ. This is disbelief and shirk.