Can executors ask for money back after it has been dispersed?

I live in Tennessee and my aunt died July 2010 without a will. She was never married and had no children. Her 2 surviving brothers petitioned the probate court to be the administrators of her estate. They closed the estate 12/2010, all documents were accepted by the probate court and monies (after expenses were paid) were dispersed to the heirs-at-law ( the 2 surviving brothers , 1 surviving sister, and the children of another deceased brother and me, my mother is deceased). I received a letter from them today explaining that they did not consider taxes being due on any of my aunt's retirement accounts or life insurance. They have chosen to pay these taxes out of my grandfather's trust account (he is deceased and his estate has not been settled yet). They are requesting that I return a portion of my funds to 'pay back' my grandfather's trust account. In my opinion, this was their error and their decision to use my grandfather's trust account to pay it. Am I obligated to return these funds? Also, would they legally be able to deduct the amount from my portion of my grandfather's estate once it is settled?