Burial requests My father-in-law died, and my mother-in-law knew his request…

Burial requests
My father-in-law died, and my mother-in-law knew his request was to be buried in a national cemetary (military). Now, 2 of his daughters have said they have a notorized leter stating his wishes to be buried elsewhere. No one has seen this leter yet, but the funeral is (of course) a few days away and my mother-in-law is worried. She does not have power of attorney, is there any way they can force a change in the burial plans that have been made?