Is it necessary to inform the beneficiaries that the gift is an ongoing charity (Sadaqah Jariyah) on behalf of the deceased father, or is the intention sufficient along with asking for prayers in their absence?

The preponderant opinion is that the deceased benefits from any good deed performed by a living person if its reward is dedicated to them. This is done through the intention of the giver of charity, and it is not necessary to inform the recipient of the charity that it is given on behalf of the deceased. It is preferable for the giver of charity not to ask for prayers from the recipient, following the example of those whom Allah praised: "{We feed you only for the sake of Allah. We wish not from you reward or gratitude.}" (Al-Insan: 9). For indeed, supplication is a form of recompense.