We do not know what was your status in 2018,2019 and 2020.
The formula is you + Your dependant + Your both parents = your family size for the given year
If you were single in 2018 and your parents do not have any dependant then it is you + parents = 3
if there is any dependant of your parents the include that also any small children who are going to be in the application.
we got married in 2021 so family size 4 make sense for 2021 for my history , what about my wife's history for 2021 i guess 4 ?
what will be my wife's family size for 2018,2019,2020?