I'd like to know how he made the keystone jewel too. In fact of course he made two that could let you into the eluvian network but only one would work with the central console. I wish it had been explained how he had the knowledge and no one else did. Also want to know if it was a slip of the pen for Imshael to have said the last time the eluvians worked was at the fall of the Dales, not the fall of Arlathan as Morrigan states if there is no Kieran. So if they did work at the time of the Dales, who was using them? I thought it might account for how the elves got to Val Royeaux so quickly and nearly conquered it and also why they risked going so far out of the Dales with their army but of course if the eluvians were being used, then how come the modern Dalish knew nothing about them, so I think it was a mistake on PW's part when writing.
I don't think any of the Dalish Keepers actually knew who Flemeth was. WoT2 says that they regard Asha'Bellanar as a vengeful and sometimes capricious being who they only go to for aid if desperate as she is just as likely to kill them as aid them. The Chasind are the same so it would seem that those groups living on the fringes of society have respect for her as a creature of magic. The Dalish probably figured out she is linked in some way to a powerful spirit but I doubt Flemeth actually admitted who that spirit was. Of course Merrill does revive her at the altar of Mythal on Sundermount, which I agree would suggest that Marethari knew. May be Flemeth had made her swear to silence on the matter; she clearly had a strong hold over Marethari considering she took the entire clan across the Waking Sea, losing their halla in the process, in order to wait where obviously she had been ordered to do so.
I wonder how much Solas knew. He talks of visiting a hut in the Korcari Wilds that is clearly Flemeth's hut, yet he seemed genuinely surprised to find Mythal was alive, which he seemed to know immediately we enter the inner sanctum of the Temple.