It is evident, he maintains, two who bring a גט are not required, etc. - אלמא קסבר שנים שהביאו גט אין צריכין כולי
Summary:
רבה can also maintain ב' שהביאו גט א"צ לומר בפנו"נ. If (according to רבה) two people are required to say בפנו"נ (because of לשמה) then if one says בפ"נ and the other בפנ"ח, it will be a גט פסול since רבה also agrees that once the חכמים were מתקן בפנ"כ it (also) needs to be said in order to prevent איחלופי.
However, when the גט is released from both their hands the רבנן certify it - הא גט יוצא מתחת ידי שניהם מכשרי רבנן
Summary:
The two לשונות in our גמרא have extreme opposite views which is the more preferable way to explain the מחלוקת between ר"י ורבנן, whether it is regarding איחלופי, or following the viewpoints of רבה ורבא.
Summary:
There is no חשש of איחלופי (according to ר"י) if the one who says בפנ"ח is a שליח and the two who say בפנ"כ are not שלוחים; however if the one saying בפנ"כ is also a שליח then there is the חשש of איחלופי even according to ר"י.