Not technically. A Neanderthal is within our evolutionary line, but it isn’t a “human” as we know Homo-Sapiens. Unless you consider Hominid on Hominid to be cannibalism.
Again not technically, as the gorilla is from a side branch on our evolutionary tree, a neanderthal however is simple a few steps down in our own line. I can’t think of a good analogy honestly.
I can’t guarantee I wouldn’t try it. I can’t guarantee I wouldn’t do a lot of things most people would find morally reprehensible so it’s to be expected.
Eating your brother is cannibalism, eating your four times removed cousin is having a nice meal, eating your cousin is kind of awkward and might be something we don’t want to talk about much.