All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
If among the conditions for being eligible for the social security payments is that you should not work or have an income other than the social security, then this is not permissible for you; in which case, you are obligated to notify the authority that provides you with the social security so that they will stop the payments for you or that they may give it to you while knowing your circumstances. Moreover, if it is possible to inform them about your work and salary without mentioning the person for whom you work – if mentioning that will cause him harm – then this is also another solution.
In any case, the fact that your brother neither takes the social security nor works does not make it permissible for you to take more than your right or that you contravene the terms and conditions of the contract with the social security authority.
Allaah Knows best.