SPOILER EPISODE 21

Why does Billie have to be in the family competition? She's not a blood Russo nor did they officially adopt her or smn. Assuming she is Alex's daughter, wouldn't she be Milo and Roman's cousin? Since Alex, Max and Justin didn't have any cousins I have no idea if all related kids give the family wizard competition or not. That wouldn't make sense if cousins have to compete yk there are so many people related to them (I know I'm not making sense but please understand what I'm saying)

Also I don't think Billie is Alex's daughter because Alex is not heartless enough to leave her OWN daughter