katakuri cannot be an emperor. He has done literally nothing, the man is so irrelevant that Morgans didn't even mention his name in the news article he wrote. Merely because he is the de-facto captain of the BMP now doesn't make him an emperor. Or else Marco would have been considered an emperor.
"emperor" isn't an official title. The WG doesn't bestow the title of emperor onto powerful people. Its just something that is agreed upon for powerful pirates.
Morgans bestowed the title of 5th emperor upon Luffy for his exploits in WCI. Given this, there's a decent chance he will proclaim Kid and Law emperors as well, as their feats surpass Luffy's in WCI.
"but Kid and Law don't have crews or territory" and Luffy was literally neg diffed by kaido post-WCI. Ultimately, the title of emperor in of itself doesn't mean much. Plus regardless of what Morgans says, the narration box might not officially refer to them as emperors until later down the line.
In any case, imo it will either just be Luffy, or Luffy, Law, and Kid. Kata is irrelevant and there's no way in hell Buggy's going to be emperor.