"He used to speak to his grandmother every morning."
Translation:Han plejede at tale med sin bedstemor hver morgen.
I checked both the most likely 2nd translation as well as the 3rd translation ("Hun plejede at tale med hans farmor hver morgen"), but the latter is flagged as incorrect. However, the English translation of the 3rd sentence would be the same, because the original English sentence does not make it explicit whether the second "his" refers to the same "he" or not. I think this makes the correctness of the 3rd answer ambiguous...
"Hun plejede at tale med hans farmor hver morgen". You wrote "hun" instead of "han".