Is this a real national championship?

While it's not an officially sanctioned USCA championship event, it is an invite event intended to gather the best 5 and Under curlers across the country.

If I win, will I go to a world championship?

No.

Do I have to be a US Citizen?

No, but you do have to curl out of a USA Curling member club.

Do we all have to come from the same club?

No, but you all had to play together at your qualifying event (at least three of you, anyway).

What if I aged out of five and under since my qualifying event?

That's ok, you qualified while you were eligible.