I'm having the same issue as a half-drow. I encountered their bodies, took the letter and both my PC and Shadowheart commented on their deaths. But when I get to the conversation with Ethel and Mayrina, the option to inform her about what happened to her brothers just isn't there. Instead of "That's Mayrina? I have bad news for her", there's only "That's Mayrina? Where are her brothers?". Never had this problem before. I also get a [Human] tagged dialogue option with Ethel in that conversation for some strange reason when, yeah, I'm a half-drow.
Another bug is during the first conversation with Ethel and the brothers, if you wish them good luck instead of saying that you'll help them look for Mayrina, their bodies simply never spawn? But if you pick the first option, they do. Never experienced any of these bugs in this questline before, so I'm guessing it's stuff caused by the new patch.