I don't think that an executor has the ability/duty to judge witness accounts. His obligation is to follow the will. If witnesses want to stand up and challenge the will, they have to be willing to go to court, fill out an avidavit, and testify before a judge that "I, John Doe, testify that the deceased told me x on this date, at this time, etc."
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I agree, a written docuмent takes precedence over verbal instructions simply because of misunderstandings. Still, that does not discount what people think they heard. At this point, we still do not have any named witnesses to Fr Collins' change of heart. Witnesses aren't allowed to stay hidden. If they want to change a public docuмent, they have to be willing to testify publically. Fr Cekada's emails don't count.