If you are in the U.S., I think you had better go visit a law library in regards to grandmothers rights when the father is still alive. NO state in the U.S. gives a grandparent what Arthur is asking for especially when the father is fit. I do not know who is advising this woman but all they are seeing is $$$ signs. It was the same with Stern, he only wanted her because she may be worth money.
If Arthur had been in constant contact with Anna and there was no estrangement between them and Anna had written in her will she wanted her parents to raise her kids in case of her death, then yes she would get her but that is FAR from the case here. Arthur has NO claims whatsoever on this child and needs to back off before Larry tells she isn't going to ever see her. Grandparents are kept from their grandkids all the time and there isn't a thing the courts can do.
Larry has family who will be given guardianship is something should happen to him and adult children die all the time at the hands of someone else, that does not mean a parent can sue the person responsible. I am sure a new, legal will will be drawn up as soon as he is given custody. Stern's version is not valid so it won't stand up in a court of law, he can ask Larry till he is blue in the face to be in charge of her money. Larry is a very wise man and he will make sure a lot of things are done for the welfare of his daughter. He and only he can make all and any decisions regarding her now and everyone else needs to shut up and stop giving him a hard time.