I'm assuming that, since they're AI's and their bodies are just a bunch of programmed polygons, they can control their appearance. Therefore, for whatever reason, they changed their appearances. Maybe TV Heads became a fad. Maybe they all swapped personality data and gained attributes from each other. Maybe they're reincarnations of their namesake and not the same exact AI's. Or maybe their old bodies just aren't compatible with R:2 in the same way R:1 PCs aren't. We can only speculate.
As for Tartarga, he seemed quite intelligent. I don't see why, with the help of Net Slum's Master, he couldn't merge with the server. Aura did it with the entire game all by herself.
I demand you come up with a source for any word in that sentence.
I'd get a video citation, but Youtube is acting pretty gay. It's the cutscene where Kite and Blackrose first meet Tartarga, and Blackrose asks about the AIs. Tartarga then describes how their nature, some of them being hackers who lost their way, wandering the network, and he uses the exact words of "Yes, the same fate as Harald."
And since Harald is DEAD...
Maybe they split off, who knows? Not us, because nothing explains it.
Completely unfounded. I'm going to go with the simpler and more likely explanation implied to us by the game itself.