I'd reckon the Alvin/Grandmaster identity crisis is more easily explained as a ruse to start the mob into hysteria about the Prophecy. The lost boy mentioned in Chapter V could be the original Alvin that the Grandmaster used to kickstart the political battle, all the information relaying back to the GM and used against Geralt as emotional collaterol, which Geralt dismisses as words once he's in dialogue with the KotWH. With the Grandmaster alluded to knowing Triss a bit better than the other Officials, maybe the Sisters are more conceited in the aftermath of the Nilfheim war and Triss an effective agent in a more ellaborate plot.
Personally I dismissed the whole temporal loop thing, there were too many political aspects for that scenario and I feel it'd be tantamount to the "t'was all just a dream" ending type.
Noting the former, it'd be a strange case of Babysitter blues for the GM to "know" Triss. In the end (at least the Neutral ending) Triss became the new advisor to Foltest, a very prestigious post, in unusual circumstances.
I haven't played TW2