It sounds like some of you have turned on the "Use home time zone" setting in the Calendar app, but then changed the home time zone to wherever you traveled to while you were there. Consequently, when you returned home, the calendar is now showing you both calendars (where you traveled to--which it thinks is now your home time zone) and where you are now (actually at home).
The proper way to use the "Use home time zone" feature is to set the home time zone to your actual home's time zone and leave that setting alone. Then when you travel, if you need to adjust the time zone, do so in the System Date & Time setting ("Automatic Date & Time--Use network-provided time" works for me). If the automatic setting doesn't work for some reason, you can adjust the timezone with the same system setting without affecting the calendar's "Use home time zone" setting.