Teams in challenges can be any size (no limits to the number of users that can be part of a team), and teams do not need to be the same size because Wellable ranks teams by average number of Wellable Points for all members of that team. The average will include team members that have earned zero Wellable Points.
Also, if a user is added to or removed from a team, his or her Wellable Points will retroactively apply to the teams average Wellable Points that are used in the calculation of team rank. For example, if a user is added to a team in the middle of a challenge, his or her Wellable Points prior to the date they were added to the team will count towards the average Wellable Points for the team.