Related for Megillah 4:1
הַקּוֹרֵא אֶת הַמְּגִלָּה עוֹמֵד וְיוֹשֵׁב. קְרָאָהּ אֶחָד, קְרָאוּהָ שְׁנַיִם, יָצְאוּ. מְקוֹם שֶׁנָּהֲגוּ לְבָרֵךְ, יְבָרֵךְ. וְשֶׁלֹּא לְבָרֵךְ, לֹא יְבָרֵךְ. בְּשֵׁנִי וּבַחֲמִישִׁי וּבְשַׁבָּת בַּמִּנְחָה, קוֹרִין שְׁלֹשָׁה, אֵין פּוֹחֲתִין וְאֵין מוֹסִיפִין עֲלֵיהֶן, וְאֵין מַפְטִירִין בַּנָּבִיא. הַפּוֹתֵחַ וְהַחוֹתֵם בַּתּוֹרָה, מְבָרֵךְ לְפָנֶיהָ וּלְאַחֲרֶיהָ:
One who reads the Megillah may [either] stand [or] sit. If one read it or two read it [together] they have fulfilled their obligation [and we do not say that two voices together are not heard as one. For since it (the Megillah) is beloved of them, they concentrate (on hearing it).] In a place where it is the custom to recite the [concluding] blessing, he does so; (where it is the custom) not to recite it, he does not do so. [But in all places, he must recite three introductory blessings: "al mikra megillah," "she'asah nissim," and "shehecheyanu," both at night and in the daytime, the reading of the day being the essential one, viz. (Esther 9:28): "And these days are commemorated and celebrated." Some hold that since he recites "shehecheyanu" at night, he need not do so in the daytime. And this would stand to reason.] On Monday, Thursday, and minchah on Shabbath three men read, no less and no more, [and there is no haftarah reading in Prophets, so that the congregation not be imposed upon, these (Monday and Thursday) being working days. And with minchah on Shabbath, too, (there is an imposition), it being close to dark and it being their custom to learn the entire day. And for this reason, too, there is no haftarah reading)]. The opener and the concluder in the Torah (reading) recite the opening and the concluding blessing, respectively. [The first one to read in the Torah recites the opening blessing, and the last, the concluding blessing. And all the others who read in the Torah (between them) recite neither an opening nor a concluding blessing. But nowadays, the custom is for all to bless before and after — a decree, by reason of those who enter (in the middle of the reading), who, not having heard the blessing of the first reader, might come to say that there is no opening blessing for the Torah; and by reason of those who leave (in the middle), who, not having heard the concluding blessing, the first readers not having recited it, might come to say that there is no concluding blessing for the Torah.]