According to FS rules as stated in the Kingdumb's Ministry 2009-2010, the visit can and will be counted only by the person who initiated it (in case 2 KW study with a person). They both report the same time, but only one of them can report the visit and the study. Usually, the JW who initiated the study is the same as the person who leads it. Exceptions are the cases where a pair of male JWs encounter a woman in FS. In this case, they can initiate a study at the door and one of them can come back accompanied by a sister. At the next encounter, the sister will lead the study with her head covered (if the man decides he does not want to get involved much; this happened for example when I was a shy, unbaptized publisher) or with her head uncovered if the man will "symbolically" lead the study (say the prayer and pose the questions from the bottom of the pages). In this case, the male JW (who was in the pair that initiated the study) can report the return visit and the female JW that leads the study will report 1 study. If next time she goes accompanied by some other JW (male or female, regardless), she will report both the study and the return visit. Of course, a study counts as 1 on the monthly report, while return visits can be counted as they are done.If a study is held on a weekly basis, 4 return visits are counted. The return visit in counted even if the study was not held (the person was sick, was unavailable, etc.) as long as the JW pair met with the person or with a close relative who lives at that adress. The JWs consider that their mere presence at the door at the convened time is preaching-work.
According to other rules, it is recommended for brother Y to go into FS with sister X no more than once a month. Only married and engaged couples are allowed to go into FS together as much as they want. Courting couples can go together more than once a month, but not quite every day.