I would contact the council for the area your daughter lived in, and ask to speak to the team involved with Child Protection/safeguarding. They may know what's going on, and where they have gone.
Wherever your GD is living, the local social services team need to be advised of the ongoing situation
They will, generally, be able to point you in the right direction of a solicitor that deals with family issues.
As others have said, also contact the police dealing with your daughter's death, and tell them of your concerns around your GD. Let them know what your daughter said about him.
Condolences on the death of your daughter, and I hope you resolve something with seeing your GD.?
Scottish political mess. Is Devolution working?