They don't attack you on sight, but you have to enter the guild through the ratways like you did in the beginning. Karliah explains what happened and that Mercer is a lying bastard, they check the safe with all of the guild's goods to find that she's telling the truth, that Mercer is a bastard who stole everything from the guild and is for the most, the reason for it's slow death.
If we're talking about when you chase after Karliah.
Lord Hard-on wrote: I think he means if you go back before that.
There's really...no possible way to do that. When Mercer tells you to "give Brynjolf my regaurds" it's after Karliah shot you with a poisioned arrow. After that Karliah nurses you back to health and the quest to shank a Mercer starts, which includes the pardon for you and Karliah.
I was wondering this so I saved my game and headed there. Neither Mercer nor Brynjolf are at guild HQ and it is evident that none of the NPCs have spoken with either of them since you origionally dpearted w/ Mercer in tow. I actually say Brynjolf leaving the guild as I was leaving on my quest and he kept saying he couldn't talk and had something to do.
BTW at this point I had made the rubbing of Calcelmo's stone to translate the journal, but I had not turned the quest back in to Enthir.
This is juat another good example of really good story telling in an Elder Scrolls game. Yeah its a little funky that you can't tell all your guild mates what happened, but the 2 main guild characters are conviently not around to muck things up.
Apparently After being betrayed by Mercer, I immedetly headed straight towards back to the guild and noticed that Brynjolf was gone (i think) and when trying to enter dialogs with the members they constantly tell me "Not now" or 'We'll talk later' Including those who offer jobs like Vex.
The second time I did it on my Wood Elf, the enterence leading to HQ were closed off, The ratway and the graveyard. The consol commands to open them worked, but the Dialogs with the members didn't change for me.