Creating a duty rota for 20+ staff spanning a year calendar

Hi there!
We have a basic duty rota for each month, whereby each member of staff should cover at least once or twice per 2 month period (depending on their fte hours)

How can I create a spreadsheet which works out fairly the cover for each member of staff and automatically populates into up to 12 months?
Here is an example of what we currently use, which relies on each staff member adding themselves to a monthly rota. I want to be able to auto generate based on the criteria for whether they do 3, 2 or 1 duty every 2 months?

Thank you !

Oops ! Sorry! It's a bit difficult to mock it up but hope this helps a bit !!! See attached

Creating a duty rota for 20+ staff spanning a year calendar

Hi there!
We have a basic duty rota for each month, whereby each member of staff should cover at least once or twice per 2 month period (depending on their fte hours)

How can I create a spreadsheet which works out fairly the cover for each member of staff and automatically populates into up to 12 months?
Here is an example of what we currently use, which relies on each staff member adding themselves to a monthly rota. I want to be able to auto generate based on the criteria for whether they do 3, 2 or 1 duty every 2 months?

Thank you !