Does either ever acknowledge the fact that Moiraine is Elayne's "half-aunt"? They must both realize it, Lan as well, even if none of the others do. I'm not suggesting that there's anything meaningful about the fact that they don't, just struck me as odd that it never comes up.

Moiraine tries to pretend she isn't a Damodred, due to the family's bad reputation, and Elayne doesn't think much about that side of her family. It's not that odd, really ;)

I'm not so much surprised that Moiraine doesn't mention it, especially since we only have one or two PoVs from her, but she must know. I can't think Elayne wouldn't know that her father had three half-sisters and what their names are. Though I spose the only way we know Moiraine is a Damodred is from when Thom points it out, other than A New Spring...

Both of them would most certainly know that they are related, but its unimportant and as Zardi said they both have reason to ignore the fact :)