Contacting witnesses and beneficiaries

[OnTheBall]

We have reason to suspect the validity of a relatives Will and have placed a caveat on probate. We are not executors or beneficiaries so in order to try and get to what has happened is there any reason why I cannot make contact with the witnesses to make sure it was signed correctly or not, or the other beneficiaries to see if they have any information that may help? Does any correspondence have to be worded a certain way? Kind regards