Gvaz: He jumped forward in time, then iirc he jumped back in time before the witcher and grew up in the order I think. He probably changed his name so it wouldn't fuck up everything if they knew he was alvin.
It makes sense though, since it's the same guy. He didn't go forward in time again though after that afaik
Alakar: For some reason I though he took Geralt forward in time too show him the future, and then when you killed him your send back too the present because Alvin can't no longer keep Geralt anchor too the future. I guess it makes more sense if he was just shown an illusion, oh well the ending of the Grand master always confuse me with the possibility of creating a time paradox.
SPOILERS FOR TWEE:
Alvin panicked and transported himself through time. He thought he went to the future, when he instead went to the past (read the bestiary on the creatures you fight. They are basically the missing link).
When you fight Jacques, he takes you into his mind, where he tries to show you "the future" (hence seeing Vizima's ruins).
Either way, you are in his head.
END TWEE SPOILERS
