The article itself states that the a member of the clan of these men founded the Army of Islam which is affiliated with ISIS.
It is likely that other members of the family may have been involved with it also as that's normally how it works.
It also states the killings were targeted so perhaps the IDF have more information than we do or Der Speigel does.
Unarmed or not, they may still have been carrying out terrorist activities.
How does International Law interpret combatants deliberately disguising themselves as innocent civilians while carrying out warfare activities?
Has there ever been a war where a similar level of targeting and smearing of soldiers in a war has been carried out while the war is still ongoing?
That will be a No and we know the reason why this is happening in this war.