All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.
If the heirs of the deceased’s have knowledge about this debt, then you should inform them about this clearance in order not to set it aside when distributing the legacy. But, if they have no knowledge about it, then it is not necessary to inform them.
Anyway, the deceased becomes free from obligation once you excuse him, whether or not the heirs know this.
Allaah Knows best.