It's a little bit complicated to explain but I promise we will try to simplify in the future.
The scope of the team is them (members) to learn to work together as a whole. Anyone can create a team and add in that team any kind of members (free, student. or professional account). However, they will have access to the arenas according to their individual membership (free members will get free access only, student/professional will have main arena access).
On Enterprise subscription, the one who will purchase will become team leader, will have authority over the team and they get (as you know) 2 VMs and 5 domains.ctf. All Enterprise members will get full access (main arena + challenges and so on). Once a member leave the team, that member losses his rights to main arena. Leaving the team would be his own sole decision or team leader decision.
The same with Enterprise Plus subscription.
The difference between Enterprise and Enterprise Plus is the # of members (5 vs 10), # of VMs (2 vs 3).
So this is pretty much about the team/s.