Have had 3-4 threesomes in civvie life, and several while hobbying. The results are very varied....
The civvie 3-way in college was superb. Both gals knew the other and had a hankering for each other, so they kissed and sucked each other, shared my cock, shared the other girl's pussy with me, etc.
The post grad school 3-way was fun, but no girl on girl interaction, so less thrilling....
A hobby threesome with Japanese Ami and another provider was superb, because the other provider was aggressively bisexual and went down on ami so beautifully.... another threesome with Ami and a civvie g.f. Was ok, but lacked the enthusiasm between the girls that is so nice and exciting....
A mix 3-some -- provider and civvie girl -- was fun, because a lot of girl on girl and shared girl action....
But I never knew in advance what was going to transpire. Like Forrest Gump, it was guess work whether I was getting caramel or marshmallow.
So, what to do...?
The point is this, you never know who's going to be into what, unless you do know. And one way to know is to ask. 'Do you go down on the other girl?" Or, "do you suck cock with the other girl?" You may feel awkward asking, but how else will you know in advance?