I agree. Thomas is as far as I know the only sibling NOT to appear, though I guess he might be the drunken philanderer Nathaniel refers to at one point, but they could have done so much with this. The Couslands and Howes were so closely aligned for years, and it seems pretty odd Human Noble never even saw Nathaniel before. They give special dialogue in both DLCs when a Dalish elf meets certain party members; so why do so little with a character like Nathaniel... I guess it would have been more work rewriting him so he knew one particular Origin, but it could be pretty neat. Wouldn't have to be much more than the special treatment Wynne gives a mage warden at Ostagar and subsequently in asides.