I'm going to make up a fake friend group
Why do you need to make up a fake friend group? Have you already named it?
My imaginary group is called "We hate you and we want you to die"
I do feel that you need to get some help about having an imaginary group that are hateful, as it can be very dangerous for people living with your or around you if one day you aren't able to discern imaginary from reality. What I suggest you do is try to get professional help as you may have an underlying medical condition.
What, I'm just making a joke and you don't have to take it seriously. You are being too serious and you should lighten up.
I am quite relieved that it was just a joke but having mental issues such as having imaginary friends shouldn't be joked about and people are actually having problems with what you have described so I recommend that you do not joke about this matter again.