How many guards were there in ancient yamen?

You mean those people standing in the lobby, leaning on sticks, always shouting "mighty"?

In the TV series, it seems to be one side 8, two sides 16.

However, there should be no hard and fast rules on the number of guards in yamen in history.

In the history of a county government, four people, including the county magistrate, were paid by the court: the magistrate, the county magistrate, the county commandant and Zheng Xue. Other civil servants, including six housekeepers, were appointed by the county magistrate after reporting to the court. The salary is also paid by the county government (a part will be withheld from the tax every year for the daily expenses of the county government), while the following officials are completely recruited by the enterprise, and everything is decided by the county magistrate or county commandant.