if his wife worked she would cease as carer. your brother can of course apply to be the carer to get carers allowance and any household benefits. Carers allowance is means tested so the wifes income would be taken into account, if wifes earnings were over certain limits brother wouldnt get any payment. I dont know if you could just swap over, a separate application probably is the way it works, but I know from personal experience that from application it can take 3-6 months to get carers allowance. Carers benefit, if you qualify, is not means tested but based on your PRSI contributions.