The timeline may or may not fit, depending when Redemptions occurs in relation to Mark of the Assassin. And I'm not 100 percent sure if either has been established of happening before the other.
At the end of Redemption it is hinted that Tallis is going to abandon the Qun. In MotA, she's acting to protecting the Qunari and (if I'm remembering correctly) she was going to use her actions to help bring her back into the good graces of the Qunari, which would indicate it happens BEFORE Redemption - where she is redeemed from her position as Athlok and again made Tallis for her mission.
Also Dawn of the Seeker is unclear. The mention of Kirkwall (as clarified by David Gaider on Twitter) is in reference to the deposition of the former Viscount Perrin Threnhold and not specifically to Anders. However at the end she receives the book, which appears again in DA2 hinting that it occurs after. It could be a different book or it could have been filled in at a later date, again, it's unclear.
Or, it could be continuity errors. But concerning the Fiona/Alistair issue, a conflict like that doesn't explain the Goldanna issue (addressed in my comment to Suenus above).
Another hitch is the whole Goldanna question, however. They supposedly share a common mother. It could be that she was paid off to pretend that her and Alistair are kin, but from the conversation you have with her during Alistair's companion quest, it doesn't seem like that explanation makes sense.
She has no reason to keep pretending that Alistair is her half-brother.
If you don't get all the upgrades for Vigil's Keep and you choose to save Amaranthine, the keep is overrun and everyone is killed. Therefore, every Awakening companion may or may not be dead, depending on your choices.
I've done some looking into the Fiona/Alistair question, and while it seems logical for that to be the mother/son relationship, apparently the timeline doesn't exactly work. Although the other pieces fit - raised as a human, son of Maric, looked over by Duncan.
Well if those initial "leaks" are to be believed, you may get up to 10 companions. That would bust the whole thing wide open. The other trend, however, that you see is there's one "good" mage and one "bad" mage - Wynne/Morrigan and Anders/Merrill.
I love Jowan, but unfortunately since there are a couple instances in which he can be killed on-screen, I can't see how they would justify it. That'd be more of a stretch that Anders and/or Leliana magically coming back to life. Sigrun too, has the possible death issue from Awakening.
Charade was OK, hardly memorable, however. She had what, maybe five minutes of screen time. On top of that, her character design was pretty gross with the heavy makeup. They'd have to do a significant redesign.
I think Tallis being modeled/voiced by Felicia Day is a strike against her reappearing. Not that she's a mega star or anything, but somehow I don't see it working out.
Also, I personally thought her performance was pretty lackluster in that DLC and hope she's not brought back.
First Enchanter Irving is alive and well in Asunder, which occurs after Kirkwall. So I'm taking that as a canon source, negating any decisions from Origins in the same way that Wynne is alive in that book, even if you killed her in the game.
I had some trouble tracking down information on Eamon. In some epilogues I know he is in Denerim and then later leaves Redcliffe to Teagan. I couldn't recall if there was one instance where he dies. In the second child epilogue, it says he visits the child often in the Circle but does not mention him dying. As far I can tell, in every epilogue, Eamon is alive.
You are right about the Isolde one, however, and I'll have to update that.
Probably need to add the same note as with Varric, that (although I can't remember now) it's unclear whether the frame of DA2 (Varric and Cassandra) comes first or the comics.