a/ “every two weekends” and “each two weekends” have the same meaning?
b/" at every two weekends" and “at each two weekends” have the same meaning?
c/“at every two weekends” and “every two weekends” have the same meaning?
d/" at each two weekends" and “each two weekends” have the same meaning?
e/“at each two-weekend afternoon” and “at every two-weekend afternoon” have the same meaning?
f/“each two-weekend afternoon” and “every two-weekend afternoon” have the same meaning?
To specify the time of the day, you can add: In the afternoon, for example. Yet, it would still be confusing. Is it only Saturdays/Sundays or both days?