[Well, the idea that Lord Death over there has a kid isn't really anything too out of the ordinary, at least not as far as pantheons go - plenty of belief systems involve the children of deities as well, and what she's describing sounds polytheistic, given that she's explicitly referred to "the god of death" and not just a singular god.

Ishimaru spends literally all of his time studying; mythology and theology and the like had to come into play somewhere along the line, even if he doesn't believe in such things himself.]

I wouldn't say that it implies that, necessarily! Knowing that the afterlife will be peaceful will likely give you no qualms when it's time to face it yourself, right? That can only contribute to your ability to have courage in this life!