To better cooperate with your teammates you can share timelines you create or have admin rights on. To do so, go into the timeline, on the top right corner there is a "share" button. Press it and you will be able to see who already has access to the timeline and what role they currently have.
Click the search field and select from the suggestions or start searching for a group or individual you wish to add. Select the appropriate role you wish to give them and press add.
In timeline settings, you can see who has access to the timeline, which access level they have, who created the timeline and export data from the timeline. If you are an admin user you could tag and also share the timeline with others or remove people from the timeline.
To see who has access, press the images of users and a list of users should appear. If you wish to see who is part of a group, just press the group and then press the "i" on the right side of the group name.
If you are an admin you could also change the access levels on others by following the steps presented over and viewing the person/group you want to change the access level to, and then change it to the appropriate level. Admins can also remove others from the timeline. Only admins can change access levels and if there are more then one admin, they can change the access levels on them self or other admins.