Is it necessary to pay expiation on behalf of my brother who does not fast?

We have answered your previous question in Fatwa no. 119664. As for his not fasting, if he was sane and able, he must make up for the fasts he missed, and offer expiation for breaking the fast by intercourse. If he was not sane, there is no blame upon him. In the case of continuous inability to fast, it is permissible to feed the poor on his behalf, with his permission.