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.
The person is asked to manage his money in the way that pleases Allah. The Prophet
informed that the person will be asked on The Day of Judgement about his property, how he gathered it and from where he earned it. At-Tirmithi
reported from Abu Bazrah that the Prophet
said: “Son of Adam will remain standing on the Day of Judgement till he is questioned about five things: his age, how he spent it; and about his youth (body) as to how he consumed it; and about his wealth from where he acquired it and in what activities he spent it, and about his knowledge and how he utilized it” [At-Tirmithi]. Islam urges people to spend their money in all good fields. So, the person should spend on his family as he should give alms to poor and needy people. Allah grants a great reward for alms given to needy relatives as they combine Sadaqa (alms) and Rahim (kinship). So, whatever, the dear questioner gives to her brother to spend on himself and on his family, or for any lawful purpose is highly rewarded. But if her brother wants to invest this money in any unlawful field, then she should not send him any money as doing so would mean helping him in sin and transgression, and Allah Says (what means): {… but do not help one another in sin and transgression …} [Quran 5: 2]. So, if this man is going to open a café where men mix with alien women or where any forbidden act is committed, then he should not be helped. Rather, he should be exhorted to invest in lawful fields.
Allah knows best.