really great questions! a big part of the game experience is that information overload. notifications are blaring with hauntings, investigators are themselves narrating what they're seeing, and ghosts are hopping in and out of rooms with their haunts. to play this game is to embrace the huge chaos of a haunted house. there will be quiet moments and loud moments that emerge naturally. as a player, it's impossible to know everything that's going on, and it's a feature!
if multiple investigators are in the same room, in playtesting, they settled and focused on the haunt, working together to see what the deal was with the haunt.
the note about dominant players is a good one, and that's a problem that arises at any game, especially a really freeform one like this. for that, why not institute this (in development rule): when a ghost is typing, and an investigator sees "ghost is typing...", the investigator may not speak.
another in development optional rule is that if a ghost @ mentions an investigator to a new room, the investigator may not speak until they leave the room.
those are a couple strategies for the game to manage dominant players, but in my experience, simply leveling with them and saying: hey this isn't going to be like a traditional game, you need to be listening as much as you are speaking. weirdly, having push-to-talk enabled is a neat externalization of "me time" and makes every word (for me at least) intentional.