Does the witness need to know that they are signing a will?
No. Under the relevant legislation a witness does not need to know that the document is a will, nor its contents. In other words if a witness was unaware that the document was a will, the validity of the will won’t be affected, providing it was executed according to the formalities as prescribed by the applicable legislation.
There does not need to be any “publication” of the will as used to be required. Publication of a will in this sense meant that the willmaker (testator) had to tell witnesses that the document was his or her will, but this rule has been abolished. Reform of the law changed this. It was thought that people should be able to say what they wanted and have it documented, without having to tell those witnessing what it was all about.
After all, if called upon to do so following the death of the willmaker, witnesses must be able to verify that they saw the willmaker sign the document voluntarily and that the signature was theirs. Or in cases where a willmaker is unable to physically sign, they directed or authorised someone acting on their behalf to do so.
Can an executor and/or trustee be a witness?
Yes. The law provides that if an executor and/or trustee witnesses the will they are not prevented from then acting in those roles. See an example from South Australia below. However to avoid problems they should not be a witness if they are a nominated executor, trustee and a beneficiary as well; as is typically the case between spouses and partners.
South Australia
In South Australia the statute on wills provides for an executor of a will to be a witness to it. Section 19 ‘Executor to be admitted a witness’ of the Wills Act 1936 (SA) states:
No person is on account of being an executor of a will incompetent to be admitted a witness to prove the execution of that will or its validity or invalidity.
Tasmania
Wills legislation in Tasmania is similar, see section 8 of the Wills Act 2008 (TAS).