A powner of attorney would normally allow the Attorney to make payments from bank accounts and the payments would normally be anything that the person would have done himself if he were able. I can look at the power of attorney for you if you scan it to me. However you say that your brother doesn't want to benefit from the estate and wants it to go to you. All that has to happen here is that he renounces his legacy, it will revert to you and presumably that would mean that the request for repayment by the executor would be withdrawn, depending on whether there are other specific beneficiaries or not and if so what they have been left. Happy to discuss further. I hope that helps. Please leave a positive rating so that I am credited for my time.
Can you clarify what your concern is about a Deed of Variation? The spouse and great nephew only inherit in the event of a predeceasing beneficiary. If the brother simply renounces then he would be treated as predeceasing. A Deed of Variation is the correct way to proceed to enable you to inherit.