You can assign a task to a user group so that all users in the group are assigned the task at once. You can also set a limitation whereby the first task status that is set cannot be changed by other users in the group.
When you assign a task to a user group, each user in the group must have a project role that includes at least the View My Tasks user right.
A user can have more rights as an individual than as a member of a group. For example, if a user is assigned task approval rights as an individual and is in a user group that is assigned only task review rights, the user can be assigned tasks as an approve task user, but the group cannot.
When you create a task and assign it to a group, you can select First vote counts for group. The first user in the group who sets their task status sets the status for the whole group; no other members of the group can set or change the task status.