There is clearly some doubt that the will was witnessed correctly in accordance with the statutory provisions. Perhaps someone is claiming that the will is invalid, perhaps there was no clause reciting how the will was witnessed, or perhaps the probate registry have queried something as the signature is odd. As this is the case, the only people who can give evidence about the circumstances of the execution are the people present at the time and the most obvious people will be the two (or more) witnesses. I suspect the witness is going to be asked to either make a statement or to make something called an affidavit of due execution (ie to swear a document to say that exactly what was done and how). This is not normally required, and only happens if there is a potential problem.