Hi. I'm an old member thatchecked back in because I wanted to talk about the show (and the books, lol).
About the battle, my take is that the 4 black sisters that joined in had discussions of what to do if Liandrin was outted. They being BA had used the power as a weapon previously so we're more proficient in doing so than the average brown, grey, white, yellow, or even blue(the reds who would also be skilled were excluded). So it was really 4 against 5 or 6( not sure if Alanna is a sitter) with a bunch of "civilians " around. It was also quite a shock to find out that 4 sitters were black.
On Verin, I think she knew that Naomi was black. I imagine she was charged with getting her into the depository. She definitely was ready for the attack and blocked most of it. I don't see any problems with cognitive dissonance regarding her actions as it is clear that not all dark friends are following the same sets of orders. She is sufficiently shady in her actions and words to be effective in maintaining her cover.