In a comment to the last post, Yehuda wrote:
"That the מקור ברוך is fictitious is obvious to any casual reader of the book. I personally began reading it with the assumption that it was reliable history but after a while I saw that the stories did not ring true. For example, he claims that the name Epstein comes from Benebashte and the he's a descendant of the כנסת הגדולה (I don't have the book in my possession so I'm writing from memory). Epstein is really a town in Germany. Furthermore the ערוך השולחןwas a levi and the כנסת הגדולה does not sign his name as הלוי.In addition, the מהר"ש of Lubavitch, the son of the צמח צדק spoke harshly of the גר"א (mentioned by his son the רש"ב in the unpublished portion of תורת שלום). It does not make sense that his father, הצמח צדק, would defend the gra's persecution of Chassidim."
אבל מה דפשיט ליה למר לדידי איבעיא לי
First the MB doesn't write (IIRC) that the name Epstein comes from Beneviste at all. He says that they took the name Epstein as a sort of mark of thanks to the town that gave them refuge. I refer you again to Sarei Hamaios who corroborates this info (though he may have been relying on Epstein).
You forget that the Baal HaTanya spoke favorably of the Gra. The Tzemach Tsedek may have been following him.
בכגון דא אמרינן יפה כח הסב מכח הבן
I'd also like to point out this study that demonstates that the Aruch HaShulchan takes a compassionate stance towards woman in his AS. It is possible that he had his extraordinary sister-in-law in mind when he wrote these points.