@MarqFJA87
There's no strict rule that says Gr has to be グル, I've seen a lot of instances that don't follow the general rule for katakana-romanji, even in official English translation
But if you have any suggestion/recommendation/feedback, sure, I welcome them.
Edit: I even contemplated using Gretel because English pronunciation of the "tel" part is "tal", but then I was afraid that the German readers would complain that the German pronunciation is not "tal", so I went with Gretal, close and will probably gives everyone the image of a girl's name