If my brother makes a mistake with the will and sometime in the future the IRS says there is money owed, is he the only one responsible?

If your brother makes a mistake and the estate owes additional taxes, he could be liable since he is the Executor. The IRS does not charge 20 per cent interest daily or even yearly.

The Party most likely to be responsible is the Decedent's Estate, at least for any federal tax liability generated by the Decedent or the Estate. The Executor or Personal Representative may be responsible for paying taxes out of estate assets. Greed and arrogance is a bad combination. The IRS statutory interest rates charges are approximately 3%, compounded daily.

Good question but impossible to give you a complete answer when there are so many unknown facts. Your brother, the executor, will be PRIMARILY responsible for any mistakes in the tax return of the deceased and the executing of the will. So, you and your sister do not have much to worry about. However, if he does make a mistake and underpays the taxes owed by the deceased or his or her trust, your brother will no doubt seek any money he has paid you and your sister to correct his mistake. So, to avoid disharmony in the family, I agree with you that an attorney should be consulted. As for the 20% interest rate that you quoted, that is not true. Interest on underpayments of tax is imposed at the federal short-term rate plus 3%. I assume that the rate of 20% that you are referring to is actually the "Accuracy-Related Penalty" that can be imposed on the portion of the underpayment that is attributable to one or more of the following: (1) Negligence or disregard of rules or regulations; (2) substantial understatement of income tax; (3) substantial valuation misstatement; (4) substantial overstatements of pension liabilities; (5) substantial estate or gift tax valuation understatement; and (6) transactions lacking economic substance.

It depends on the nature of the "mistake." The IRS does not charge 20% interest even per year, let alone daily. If he does not "do it right", the results can be painful for him and for you.

No, the IRS does not charge 20% interest daily. I don't remember the exact rate, and penalties can sometimes be stiff, but the interest rate is something reasonable. If an administrator is negligent in the handling of the tax returns for the estate, then he is liable for that error. The most likely possibility is that the IRS would come after the estate as to any mistake your brother made, and your brother would owe the estate for the loss caused by his negligence. If the IRS came after the beneficiaries because of any such negligence, however, then the beneficiaries likely would have a claim back against the administrator.