One issue with this scenario is that I have an overview of everything but in reality don't know how much I am supposed to know.
Since I would have to challenge the will on grounds against Aristoteles, it is known that Plato has dementia and has a damaged left hippocampus, therefore at anytime prior to the stated recovery he was without testamentary capacity. Aristoteles naturally has agreed to this because he has stated that there were no signs of memory problems, as a supportive statement for why Plato was with testamentary capacity during the signing of the will.
Given the witnesses are supposed to be partly the evidence, they must have been there during the signing of the will or their support is invalid. Therefore we can infer that for starters, Plato did not write this will themselves under testamentary capacity but merely signed it.
It's unlikely that someone who has died of natural causes would sign a will they did not create and subsequently die shortly after. Furthermore, signing a will on it's own does not demonstrate testamentary capacity, therefore the evidence that Plato was with testamentary capacity at that instant he has signed the will and not simply afterwards, is in need of proof.
For starters this puts even ground in place.
Based on the earlier statements, either the witnesses went with Aristoteles on holiday and Aristoteles did not mention this, to witness the signing of the will, or they all went to Plato's house and signed it there. I would know being Plato's apprentice that there was no period prior to this where he was of testamentary capacity sufficient enough to sign a will.
For starters at this point I have made it clear that Aristoteles either has been lying or hiding things.
Now in reality, this entire case would have been more in an attempt to make Aristoteles mess up by saying things he really should not due to the fact that he is lying in the first place. The evidence would be much easier to acquire too, simply by having police check relevant cameras, and asking particular neighbors on the activities of the witnesses during these periods.
As a scientist using science, the evidence is much more extensive.
There are quite a lot of unlikely things, and oddities, but this achieves the goal since there is no evidence that Plato was of testamentary capacity, but there is evidence that they were not prior to signing the will.
One could even say that because they were not of testamentary capacity at the start of the holiday, this counts as kidnapping. To refute this Aristoteles can only state that they signed the will before the holiday and were of testamentary capacity throughout it. This therefore depends on whether I the apprentice have had contact up to the kidnapping of Plato. Either way, this restricts the amount of choices Aristoteles and the witnesses could have made and provides more parts to investigate.
Would be my take on it without saying the obvious scientific points.