Can a biological custodial father grant shared custody to a grandparent? Must the non-parent be notified of this court ordered modification?

No.  Unless the other parent's parental rights have been terminated, they have a right to legal notice of any change in custody. This answer is given in accordance with the laws of Virginia and may not be applicable in any other state.  It should not be construed as legal advice, as that would require a more thorough analysis of all of the facts involved in a specific case.  If you need further information or assistance, please feel free to contact my office for a consultation. Case results depend upon a variety of factors unique to each case. Case results do not guarantee or predict a similar result in any future case.