I sometimes make interrogative sentences that end up having double "not"s like,
Isn't it not that great? (I think it's not that great)
Shouldn't it not be there? (I think it shouldn't be there.)
Couldn't you just not do it? (I think it was/is possible for you not to do it.)
In writing, I often rewrite the sentence in different form, since it feels not quite correct, but those kind of sentences come up in mind occasionally because that's how I'd naturally say in my native language.
Are those kind of sentences at least understandable, if not correct, or do native speakers also say like that?