The 他に(も)・他(に)は grammar point 395 has a variety of possible forms:
他に ・ 他に(も)
他は ・ 他(に)は
他も ・ 他の ・ 他を
But there is no explanation when to use which. So this is my most hated grammar point since I have no clue how to answer the reviews and I’m just guessing.
Besides that, your accepted answers are sometimes contrary to the linked readings. For example for nouns following ほか you normally only accept the の particle. But the linked second reading says “に is more common and sounds more natural”. So why don’t you accept に as well in those cases?
Suggestion: for every mentioned particle in your structure you should tell when to use it (with verb, noun, adjective etc.). Furthermore you should use hints to tell the user why an answer is incorrect and why the choosen particle can’t be used in that case.