When splitting the Megillah between two people. (First reads Perakim 1-8, second 9 and 10); who makes the brachot?

ב"ה Shalom There is actually a long discussion if it is proper to begin with to divide the reading.(See פסקי תשובות סי' תרצב הערה 4) In any case, some major Poskim allowed doing so, especially when a need arises to do so. However, all readers should be present for the berachot and reading. To answer your question, , the first reader should say the first berachot and the second reader may say the Beracha at the end. (סי' תרצ"ב, משנ"ב) See מקראי קודש לרב הררי, פורים פרק ז הלכה כ"ו (מהדורת תשס"ג,הערה צא ,ושם נספח ט"ו May you have a Happy Purim