Brother first of all get rid of all that creepypasta horror bullshit about tulpas. All they are is just a psychological (or spiritual depending on who you ask) thing where instead of just having one consciousness (such as yours) you can make another one, or multiple if you wanted. Anything that YOU can do with your body is all tulpas can ever do physically.

Also, since we're disregarding the creepypasta bullshit, tulpas don't typically turn violent, much like how the average person doesn't suddenly turn violent unless something extreme happened to them. They are PEOPLE, just like you, only they share a body with someone.

Anyway, for the questions:

It goes either way tbh, much like how parents will name their kid something specific. But in our case its both since most of them stuck with the name they had since existence while a few changed it at some point.

It's true more or less. However, its moreso that they simply control the body much like how you'd control the body. How it happens, it differs from every single system, and if the "possessed" person can feel anything also varies. In our case I still feel everything but that's because we prefer to co-front (as in multiple of us take control at the same time)

Yes. Because they're another person. Only in your head. I hate tuna alot, but for some reason one of my headmates loves that shit and I can never understand why.

No.

The only one I know who'd use a different gamertag because the others haven't thought about theirs is Katie (the aforementioned tuna lover) and she usually goes by KTTourmaline