According to the Odyssey of the Mind Program Guide, the following rules apply in this situation:
In most circumstances, all team members come from the same school. However, multischool teams — those made up of students from different schools — are permitted as long as all the schools have a current membership. Multi-school teams may choose which school name they wish to use for registering their team, but they may only compete at one regional tournament, even though the multiple schools may be located in more than one region.
Furthermore, each team is allowed one student that attends a different school without a membership, but who resides in the same general area. However, the team members must agree and must have permission from principals from both schools involved. If a team member transfers to another school he/she may continue on the team until the end of the competition year, provided both school administrations approve.