#2 I have no idea, as I never did the LL storyline, but #1, isn't it obvious? It's Susan Calloway giving the player the Echo.

Seriously though, I assumed it was supposed to be whatever member of the Twelve granted the Echo to the player - an interesting retcon to this was those few lines of Answers were similar to the 'Dalamud Answers' version that much later replaced all BGM in the lead up to the game's original shutdown (maybe that singing was that deity singing through the Echo?). Or maybe I'm just reading to much into it.

#3: well, the last you hear about them is that they retired to the Alchemist's Guild to heal their wounds after their run in with Gaius during Future's Perfect, so anything could have happened to them really. In any event, I really hope Yoshi-P brings them back in ARR, as I really liked the idea of having an NPC along for the ride in those quests.