You have done everything correctly. You have reported her conduct at the correct authorities and you have created a verifiable (through the sms messages) trial that shows that you have not taken your grandson against his will.
If you are asking in relation to what you can do with regards ***** ***** grandson's schooling, how to get him to school and back etc, then I am afraid I cannot advise you. That would be a logistical issue that I cannot assist with.
If you are asking me whether you can remove him from his school and place him in another school, then the answer is yes, as long as you have the co-operation of your son, who is his guardian.
If you are concerned about the stability or the lack thereof that your grandson has to endure, then you can get relief from the Children's Court. The Children's Act state that even grandmothers can approach a Children's Court (essentially a specialized Magistrates Court) to apply for contact and care, or custody as it used to be known.
So, you can go, with or without the aid of your son, to a Children's Court and show on application that it would be in the best interest of the child that he remains with you if that is what you want. Should a court order that you be given custody, that would prevent his mother from coming to your house in the future and just taking your grandson again.
I am not sure if this answers your question. So if you have follow up questions before you rate, feel free to ask them at no extra cost. If you are satisfied with the service, kindly rate it positively