Okay, so this is pretty complicated, but after looking over everything and talking amongst ourselves, we're going to say that Kainé can have a break from Tyrann. He has enough canon to be apped on his own. If someone were to play him, the character would be given a body by the fae, because that would be hilarious to them. But they'd separate her from her tormentor because they don't really like competition and they have enough power to keep her alive by herself.

In regards to your second question, we're fine with you playing two characters from the same canon with enough of a case made for there not being any meaningful interactions with one another. So you could play a character from Drakengard 3 *and* another from Nier Automata without any problems, but they exist on the same world and they fall somewhere on the same timeline. Final Fantasy games are each their own separate canons, unless they're officially attached, like FFX/X2 and FF13 and its sequel games. As far as Tales of games go, they are also all their own worlds, except for Zesteria and Berseria. The Tales of the World or Rays/Link/Crestoria would be considered AUs, much like Fire Emblem Heroes & Warriors would be AUs of the other Fire Emblem games. Star Ocean games all exist in the same timeline, but there's enough of a time difference between each that you could play Fayt from 3 and Edge from Last Hope without any real issues.

We hope this helps you!