All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
If the maintenance of his mother is obligatory on him, like if the mother is poor, then he has no right to give away all of his wealth as Sadaqa (charity). Because if he gave all of his wealth as Sadaqa, he would waste the right of his mother. The same case applies about his sisters and brothers, according to scholars who say that the maintenance of the poor brothers and sisters who are unable to make money for a living is obligatory. It was mentioned in the Hadeeth: “It is enough a sin for a person to neglect those whom he is responsible to sustain.” [An-Nasa-i]
The jurists stated that he commits a sin if he gives Sadaqa that decreases his obligatory maintenance. The author of Al-Rawdh Al-Murbi’ said: “Giving Sadaqa from the excess beyond his sufficient limit and that of his dependents maintenance is desirable as the prophet, sallallahu ‘alayhi wa sallam, said: “The upper hand is better than the lower hand (the giving hand is better than the receiving hand), and begin (charity) with your dependents; the best Sadaqa is the one given from the surplus.” [Al-Bukhari and Muslim] He commits a sin who gives Sadaqa from what decreases his obligatory maintenance.” [End of quote]
But if the maintenance of his mother is not obligatory on him according to the Sharee’ah, nor the maintenance of any of his brothers and sisters, then there is nothing wrong with spending his wealth in Sadaqa, provided that he is not in a disease that is feared to cause his death. But if he was in in a disease that is feared most likely to cause his death, then, his donations take the same ruling of the will. He has no right to give Sadaqa or donate more than a third of his wealth.
Allah knows best.