There is no doubt Tereza caused all the shit. I do not think Regina&Sher did the right thing, far from it, but Regina was closer to Tereza long before Renata was in the picture, so when Tereza cause a conflict, where they were forced to take sides, Regina&Sher were put in a very difficult situation. I say they made a terribly wrong choice, but for them standing in it, it was likely not a easy situation. The relations with Renata might be impossible to restore, even when Tereza leaves, after their betrayal of Renata, but I mostly blame Tereza for it all.