The Sects of Atheism

[Angrboda]

Atheist: a person who disbelieves or lacks belief in the existence of God or gods.

Doesn't say anything about not believing in afterlives, ghosts, reincarnation, or souls; just gods.

Yes I agree with your definition of sects.

Your second point is incorrect because what links you all to each-other is your “lack of belief in Gods” and what links me to an Aztec priest in 500BC is our beliefs in Gods.

Third point : You can’t have an opinion on souls or afterlife which are god-related topics and then claim the definition of an atheist which is “lack of belief in Gods”.

Your third point is wrong. Beliefs about souls and the afterlife are not necessarily god-related. And it is consistent with a lack of belief IN gods to hold opinions about them. It's a lack of belief in [the existence of] gods, not a lack of an opinion about gods [and related matters]. It doesn't entail anything about a person's views about souls and the afterlife.

If this is the whole point of your thread then you've screwed the pooch. You are laboring under some logical and factual errors.