Hi Cassey.
If you have a will with only 1 signature by a witness, then the will does not meet the legal requirements to be a valid will. It is called an “informal will”.
If there is a valid will, then the process is to apply for probate of the will.
If there is an informal will, then the process is to apply for Letters of Administration with the will annexed.
For the Court to accept the informal will they must be satisfied that the document was intended by the deceased to be their will. The obligation of the applicant to meet this requirement varies from state to state. In NSW, in addition to the application for Letters of Administration with the Will Annexed, the applicant must seek a declaration by the Court under Section 8 of the Succession Act that the informal will constituted the last will of the deceased.
You will also have to disclose any previous wills that the deceased had.
If there is no previous will, then you will have to state who would be affected if the informal will was not accepted by the Court. This would then fall to the rules on intestacy and who would, otherwise, be entitled to share in the estate. If there are such persons, they will need to provide a written Consent to Administration to the applicant.
Please search your brother’s personal documents and see if you can find a previous will.
The problem can be solved.
I hope this is helpful.
Kind regards,