Never been in a threesome but I'm lucky enough to have friends to have been involved in such arrangements.
On the words of a very good friend and sexually experienced woman: if the women are not the slightest interested in being with each other, there is a 90% failure chance.
MMF trios are easier to manage. Yes, men are basic amd as long as they can put their thingy inside a hole, everything is fine. Some guys will use the woman in the trio as an excuse to "feel" bisexual territory. Others will see the other as a competitor and up their game. Usually, the woman reaps the bounty.
FFM trios are trickier. If the women are in to some bisexual interaction, it can smooth things over. If not, the guy really has to go the extra mile to be available for both and deliver. And even then, the probability to let one or all parts feeling unsatisfied is very high.
Last but not least: can't say if Buttercup is playing dirty or just being kinky but... damn.
