So there's already Leo, Piper, and Jason. The series is all about the rise of the Giants and making peace between the Greek and Roman Camp.
Juno says to Jason," The prophecy demands that we change. The giants will rise. Each can only be killed by a god and demigod working together. Those demigods must be the seven greatest of the age. As it stands, they are divided between two places."
Does "two places" mean the Roman and Greek camp? So that means the other four demigods will be from Rome. Possibly Jason's friends.