She owes accumulated zakaah. Can she give it to her brother in monthly instalments?
It is permissible to give zakaah to one’s brother if he is poor or needy, or is in debt and cannot pay it off. The definition of poor is one who has no income, or he has an income but it is not sufficient for him. So if your brother’s income is not sufficient to meet his needs and those of his children, without being extravagant, then it is permissible to give zakaah to him. But we must beware of being biased with regard to this important obligation. See question no. 21810.
Zakaah must be paid immediately when the hijri year has passed. It is not permissible to delay it unless there is an excuse or a greater interest to be served by doing so, such as if there is no one who is entitled to it or if the money is not available, or one is waiting for a relative who is entitled to it. In such cases it is permissible to delay it for a short while.
Ibn Qudaamah (may Allaah have mercy on him) said: If he delays it – i.e., zakaah – in order to give it to one who is more entitled to it, such as a relative or one who is in great need, if that is for a short time then there is nothing wrong with it, but if it is for a long time, it is not permissible. End quote from al-Mughni (2/290)
Based on this, your delaying zakaah for five years was a mistake. Praise be to Allaah Who has guided you to set matters straight and to resolve to pay it. We ask Him to accept your repentance.
If you have no choice but to give the zakaah in instalments to your brother, because you fear that if you give it to him in one go he will spend it and will be left with no money for the rest of the year, then you can tell him that you have such and such an amount of money, and this money will be a trust that you keep for him with you, and he will have so much each month. If he accepts that, then praise be to Allaah. If he does not accept it, then it is not permissible to delay the zakaah, so give him as much as he needs and give the rest to someone else.
But it should be noted that the money that you keep as a trust for him must be kept and protected by you, it is not permissible for you to benefit from it, because in fact it does not belong to you, rather it has become your brother’s property and you are enjoined to take care of it.
With regard to the coming years for which zakaah is not due yet, you can pay it in advance in the form of regular instalments to your brother or to anyone else, but that is subject to the condition that when the year ends, you work out the zakaah. If you have paid it in full, then praise be to Allaah, but if there is something outstanding, then pay it straight away; it is not permissible for you to delay it. If you have paid more than was due, then this is a voluntary donation on your part, unless you intended that it should be for the following year.
For more information on that, please see question no. 45185.
And Allaah knows best.