Grandparents have no rights of any kind at all. So the child's mother decides when and if grandparents see the child. The grand parents have no rights whatsoever to demand to see him.
If the child is autistic then it is essential that his interests come first and anyone looking after him fully understands his needs and special requirements.
You do not mention his father, Is he still involved in his life. I would go and talk to Citizen's Advice or a solicitor to be absolutely of your daughter and grandsons legal rights , so inappropriate care by this other grandmother, which may harm the child is strictly limited .
Have any of you got all electric cars? Pros and cons please.