Answer:
(Fatwa: 171/D=68/file/D=1432)
Telling a lie shall not be lawful. Thus if the requirements of mother are fulfilled with rent money and the amount given by the elder brother then you are not required to give money but you should offer her out of love and dedication. It shall be counted your obedience also and source of good reward. Then, your mother shall be free either to spend it in her personal needs or give it to her children. However, you can express it if you brothers really feel want of money.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband
