Is it permissible to collect a debt from the debtor's son if the father delays payment, knowing that the son is motherless, and would that be considered consuming his wealth unjustly?

You are not permitted to exact your right from your friend's son without his willing consent, for the financial liability of the son is separate from that of his father, based on the Almighty's saying: "And every soul earns not [anything] except for itself, and no bearer of burdens will bear the burden of another," and based on the saying of the Messenger of Allah, peace and blessings be upon him: "Indeed, no one commits a crime but against himself, nor does a father commit a crime against his child, nor a child against his father." The meaning of this is that no one is held accountable for the crime of another, whether relatives or strangers, and no one is punished for the sin of another.