They are part of a group of 230 Assyrians captured in the Khabur River Valley in Syria in February.
ISIS-Libya has been killing Egyptian and Ethiopian Coptic Christians for some time now by execution, most of which were filmed. But ISIS honestly has not deliberately killed a lot of Christians in Iraq and Syria. Maybe a few.
So if they kill these Christians, this will start a new ISIS jihad against the Christians of the Levant and Mesopotamia.