If the executor of my mothers will is my brother and he is incapacitated due to illness, how do we name a new executor? Would his POA takeover?

If it is apparent that the named executor lacks capacity or may lack the capacity to perform the duties of the executor, and the testator (the person creating the Will) is still living an has the mental capacity to update a current Will or create a new Will, then it would seem the best way to proceed is for the testator to create a new Will naming another executor. Nowadays, because of software, drafting a new Will is the preferred way rather than using a codicil to modify an existing Will because sometimes codicils are lost. If the testator does not want to update the Will and the named executor lacks capacity, upon the death of the testator, the successor executor named in the Will could offer the Will for probate and inform the court that the named executor lacks the capacity to perform the duties as the executor. If the executor did have some capacity, the executor could renounce the appointment. If there is no successor executor named in the Will, then usually another heir would offer the Will to probate and explain that the executor does not have the capacity. The court may appoint a guardian ad litem to determine if the executor has the capacity although it is unclear the court would do so. It is less likely that a person who has the Power of Attorney for the executor would be named the Executor rather than another heir. So, because of all this uncertainty, it is better for the testator to revise or create a new Will.