To check multiple calendars of colleague Carerix users at the same time you use the Scheduler option in the Calendar.
Choose "Scheduler" in the top right
Click "Calendar of" for the list of colleague names to show their calendars.
Every Carerix user gets a different colour that corresponds with the indicator on the left side below "Calendar of"
To hide the scheduler of other users, click again on their names below "Calendar of"
To show your own week- or month view once more, click the "Week" icon.