I remind you of Barry1010's post on your previous thread:
https://www.theanswerbank.co.uk/Family/Question1741845.html
If your mother can't afford to give the money away because she will need it for her care, you would be acting unlawfully (potentially risking prosecution and/or having to pay back the money to your mother's account out of your own) if you were to let your brother have it.
Do your best to explain to your mother that, if the money isn't there in her account (when it should be) to pay for her care, YOU could very well end up having to pay that element of it yourself. (i.e. in the end, it wouldn't be your mother who was giving money to your brother but you).
Either try to similarly explain your position to your brother or simply tell him to take a very long jump off a very short pier!