Sheikh `Abd al-Rahmân al-`Ajlân, lecturer at the Grand Mosque in Mecca
You have the right to grant the reward of your almsgiving to anyone you please. You may intend the reward for an individual or for a group of people.
Sa`d said to the Prophet (peace be upon him): “My mother died, and I think that if she had spoken, she would have given charity. Will she have a reward if I give charity on her behalf?”
He said: “Yes.” [Sahîh al-Bukhârî and Sahîh Muslim]
If you give alms separately on behalf of yourself, then your father, then your mother, that will be fine.
Likewise, you can opt to gather everyone together in your intention and offer a single charitable donation. This will also be correct, by the will of Allah.
And Allah knows best.
Source: Islam Today