Your situation is fairly typical except that it was a four-way. Usually, it involves a three-way w/ one guy. In the bars, the girls will readily agree to threesomes. In fact, if a BG's friend proposes a 3some, rarely will the BG say no to it. She will almost always say "up to you" even if she is making an unhappy face when she says it. They hate to deny their friend a chance to make a buck. Often, both will enthusiastically agree to it, and to get the farang to pay the BF, will grind bodies, grope each other's tits and crotches, stoop down, stick out tongues simulating cunnilingus, and pull out their friend's tit and suck it, accompanying all of this with appropriate lascivious sounds and expressions. It's a sales job.
Then when they get you back to the hotel, suddenly one or both get a case of shyness, sometimes even wanting to hide in the bathroom while you do their friend. I am convinced that sometimes one of them is really just dying to get into her friend's pants and this is the perfect excuse, but finding two is the trick. Most of the time, it is just a classic case of " bait and switch", and they are both just conning you.
To avoid this ruse, you have to be perfectly clear that when you get to the room, they will do the lesbian action first, then you and your friend will join in, AND that they won't get cent one unless they do their friend first. They are counting on getting back to the room, start the BJ action, and then it is tough for you to refuse to pay them, since they have performed a service for you. Once you've had sex with them, you owe them something, although you should dock their pay, for failing to fully keep their end of the bargain. If you are clear in your expectations and demand the lesbo scene first, then you can send them away with nothing if they fail to perform as agreed upon, and even go back to the bar and ask for a refund. It you have dropped some coin on drinks, and the owner or manager is smart and values your business, then he will refund the BF. After all, 200 Baht is only 2 or less drinks. Be prompt and polite.
Chok dee, krap !!