Is it permissible for me to give the sadaqah of my wealth to my sisters who are students? Is it permissible for me to contribute with them to household expenses on the basis that it is the sadaqah of my wealth?.
If what is meant is voluntary sadaqah, there is nothing wrong with giving it to your sisters and contributing it to household expenses, because sadaqah is broad in scope.
But if what is meant is obligatory charity, i.e., zakaah, then the matter is subject to further discussion.
Firstly, it is permissible to give charity to your brothers and sisters, if they are poor and you are not obliged to spend on them because you will not inherit from them, or because you cannot afford to spend on their maintenance.
It is also permissible to give zakaah to them if they have debts, whether you are obliged to spend on them or not, because paying off debts is not obligatory for the one who is obliged to spend on another person’s maintenance.
Shaykh Muhammad Saalih al-‘Uthaymeen (may Allaah have mercy on him) was asked about giving zakaah to one’s brother and sister.
If giving zakaah to him means that your duty towards him will be waived, such as if it is obligatory for you to spend on his maintenance, but you give him zakaah so that you save your money and do not spend on him, then this is not permissible, because zakaah cannot be paid to protect wealth. But if it does not mean that your duty towards him will be waived, such as if it is not obligatory for you to spend on his maintenance, because you will not inherit from him, or because you cannot afford to spend on him as well as your own family, or you are giving him money to pay off a debt that he owes but cannot pay off, then it is permissible for you to give your zakaah to him, rather it is preferable for you to give it to him rather than anyone else, because giving to him is both an act of charity and upholding the ties of kinship. End quote from Majmoo’ Fataawa Ibn ‘Uthaymeen (18/422, 423).
See also the answer to question no. 50739.
It is permissible to give zakaah to students of sharee’ah who are devoting all their time to that, because this study is a kind of jihad, so it comes under the heading of “in Allaah’s cause” or for the sake of Allaah.
As for students of worldly sciences and branches of knowledge, that does not come under the heading of “in Allaah’s cause” or for the sake of Allaah, but they may be given zakaah because of poverty or need, for example if a student does not have enough money to cover the expenses of study on which his finding the work or job that he needs depends. He may also be given zakaah to pay off his debts, such as if he owes money to the university; in that case he may be given enough to pay off his debts.
It is not permissible to give zakaah towards household expenses.
But if we assume that your husband is poor and is entitled to zakaah, then you may give your zakaah to him then he may spend it as he sees fit, and if he spends it on the household there is nothing wrong with that.
And Allaah knows best.