In California, the law requires a standard will to have at least two witness signatures. These people must also meet legal requirements.
If you fail to have the proper witness, your will may not be valid. The court could throw it out in probate, which means your estate would then default to the state’s rules for disbursement and not necessarily abide by what you want. It is essential to ensure you have valid witness signatures for this reason.
California Legislative Information explains you can use anyone as a witness who meets the requirements for general competency. If there is any concern over mental health or issues, then you should probably choose someone else to serve as a witness. In addition, competency requires the person to be at least age 18.
It is a good idea to choose only witnesses who do not have an interest in the contents of the will. This means they are not an heir or someone who will benefit from the contents of the will. If one of your witnesses does have an interest, then you will need to have an additional witness to avoid issues.
The witnesses must voluntarily sign your will. You cannot make them or otherwise force them into doing it.
It is important to understand the witness signatures serve as a way to validate your signature on the will. These people may have to testify in court that the signature is yours and they saw you sign the document. You should make any witnesses aware of this potential to ensure they are ok with it.