I have a Moto G5 android phone for several years, with the associated Google account. I have used the Calendar on my phone for travel, doctor's appointments, etc.
My wife has had a different Google account for several years and just recently bought her first smart phone, also an Android.
Much to our mutual surprise, when she looked at her Calendar on the smartphone, all my entries appeared!! I entered a hew event on my calendar on my phone, and she immediately saw it oh her phone.
We have both had Hotmail email accounts for many years. We may in the past have somehow linked calendars.
A few minutes later, for no apparent reason, her calendar cleaned itself up.
How can I stop this linking in the future?