How to make a child visitation calendar

I would like to make a visitation calendar for my child for myself and my ex-wife that can be shared and easily be modified by either parent as the days that the child visits each parent changes. But don't know how to get started. Couldn't find any templates online for numbers. Noting the visits on my phone calendar is a bit grueling especially if I forgot to note a change. This causes problems similar to missing a doctors' appointments. Someone is late or visit needs to be rescheduled, etc. I found a template for excel but the formulas didn't convert when opened in numbers and I am less familiar with excel. I've attached image of that template. Any help would be greatly appreciated.