I love, love, love this. It brings such depth to Elwing, whom I already like. It takes her following Earendil - and being turned into a bird, for heaven's sake - and makes it more realistic. We can imagine, perhaps, that the chroniclers of the QS in-universe changed Elwing's actual leap into something divine and Valar-sanctioned.

Seeing your AU-Elwing from an outside perspective is quite illuminating; it's quite clear that she's broken and not yet ready to heal, and that perhaps her healing won't ever include her sons, whom she saw as having irredeemably betrayed her and vice-versa.
You've done a great job of showing the radical difference between the twins' and Elwing's expectations of each other/their justifications for their actions.

I think you captured Elwing and Faeleth's rather volatile dynamic perfectly. There's a similar dissonance there: push-pull, withdraw-protect, not just on Faeleth's part but on Elwing's.

My heart breaks for the twins, too. The part about their conversations about Elwing was just perfect.