If a person is reading Megilla for his wife or a group of women, and he himself has already fulfilled the mitzva, should he make the brachot? Rav Yosef cites the debate between the Ramo on one side and the Pri Chadash and the Gra on the other, with both saying that a bracha is made, but the Ramo claiming that the bracha is lishmo'a megilla, and the Pri Chadash and the Gra saying that it is the regular bracha of al mikra megilla. Interestingly, there is one view that claims that no bracha should be said at all in this situation, since it is unlikely that the women will be able to pay full attention for every single word, and since the reader has already fulfilled his obligation, the brachot will not be said for anyone who pays attention to the entire reading. However, Rav Yosef completely rejects this approach, based both on the Gemara in Megilla 19a which says that you make a bracha even when reading for people who do not understand the text, as well as based on the logical point that women today are quite learned and thus likely understand every word. Thus, he concludes that the regular brachot should be said.
With regard to the bracha after the reading of the Megilla, Rav Yosef rules that since it is a minhag to recite it, it should only be said with a minyan, because only with a minyan do we have a fulfillment of pirsumei nissa. In a footnote, he points out the view of Rambam (Teshuva #84)who says that one should not even say Amen to such a bracha, as one should not say Amen to a bracha which is doubtful whether or not it should even be said.