Since in the case of the Thieves guild, you are all on the same side so it can be up to you if you have known each other or not. You may have done work together in the past, know each other by name. It is as you said, up to you decide if you want to be acquianted or not with each other.

In cases of the other groups it is more possible they would not know each other with the exception of Therus. But that too is up to them to decide if they want to know each other or not.

Since everyone from the RP is used to having a OoC thread, I will ask if you wish to have one for cooperative matters. I have no objections to it myself, I can make one for each of the groups that wish to have one. Otherwise you can PM between each other or just play it impromptu.