To bring the bear-rug into this room as well: I only just realised how truly atrocious this whole larger brothel situation can be for Astarion & Gale if you line up events in the right (or the very wrong) way.
In Rivington you can first meet Tara and make date plans with Gale (I am not sure if friends also get an invitation to dinner). The murder trail then leads you to the Flophouse where you meet Astarion's siblings and learn more about the ritual. From their you are lead to Sharess' Caress, where Madame will gift you with a stint with the Drow twins for solving her employee problem. (Alternately, you can also start with Madame and wrap it up from there.) Should Halsin be in the party, he will make his interest to join you with the twins known, not matter whether or not you have shown any interest in him before. If you progress the "Agreement? What kind of agreement?" line of dialogue both Astarion & Gale will make their disinterest known, for Astrion it ends there (as this is Pre-Cazador) for Gale you can either mock him or make him go through with it. Also there is an option to go alone with one of the Drow which Gale will also not like but apparently he is not allowed to do anything about it either.
So after having established that both guys don't have much to offer in regards to sex (because one has "complications" and the other is boring) you move on, coronations happen, contracts are changed, eventually Halsin makes his moves with the "many lovers" speech which may or may not be motivated by an orgy or at least the thought of one. So in this scenario, Astarion's reply is very hard to read as anything but fear of loosing the PC, while in Gale's case you can either dump the "boring guy" for the hot druid or are left with the feeling of having chosen the stable but dull relationship. All around lovely.
And the reverse card for SH. You can progress Rivington and show up in sharess caress where she declines to sleep with them(until you have first time with her). Game also always puts Halsin's offer before her scene, so there you can decline his "offer" in the most hard way(deep rothe line) and he is gonna be chill for some time, however after her scene you instantly get Halsin's banter proposing threesome in the morning into Sharess' caress ridiculous thing. It's like reverse Gale situation almost.
Thats why I say this thing in brothel and Halsin overall should be somehow tweaked for all the companions.
