All perfect praise be to Allah, The Lord of The Worlds, and may His peace and blessings be upon our Prophet Muhammad and upon all of his family and companions.
The father is permitted to take back any in kind gifts given to the son according to Islam for An-Nu'man bin Bashir (May Allah be pleased with him) narrated: His father brought him to Allah's Messenger (PBUH) and said, "I have given this son of mine a slave, who was belonging to me." Allah's Messenger (PBUH) asked, "Have you given all your children the like of him?" He replied, "No." Allah's Messenger (PBUH) then said, "Take him back then." [Related by Moslim]. Yet, this is regarding in kind gifts but as for canceling the remission of son's debts is impermissible.
Furthermore, Al-Imam As-Shrbini (May Allah have mercy on his soul) said:” The father is permitted to take back any in kind gifts given to the son, but as for cash whether it was given as a debt or not, he isn’t permitted to take it back in both cases, because the debt is no longer exist as is the case with gifting him something and being worn out.” [Mughni Al-Muhtaj vol.3 pp.568].
Therefore, the father isn’t permitted to cancel the remission of son’s debts because he already free his son from the liability to defray those debts in accordance with the juristic maxim:” taking back debts after being remitted isn’t valid” so fulfilling the aforementioned bequest isn't obligatory, but the son is recommended to give charity as much as possible on behalf of the deceased father. And Allah knows best.