Hi, i'm new at this. So ask questions if i haven't explained it correctly.

I have two deceased grandparents. Both were born in Europe and became German citizens. They then went to South Africa to start a new life after world war II and had my father. 18 years later my father enrolled in the army and my grandparents returned to German. Where they both lived happy lives together. Until my grandfather passed away about 5 years ago. My grandmother then decided to spend her remaining years with family in South Africa. Until she passed away last month. Now, I currently have a two year visa for the UK and would like to know if I am eligible to apply for a German passport or ancestral visa.
Where is the best place to go to get this info?