New York
Your question on threesomes caught my eye as I sit sipping my evening single malt since, as it happens, I have one scheduled for the coming week. So, FWIW, here are a few reflections on the subject from my years of life in this hobby (well, actually 18 months but it feels like a decade 
An MFF threesome is the stuff of dreams for many hobbyists, the stuff that porn is made of. Still, I find that it is an excursion I can take bring myself to take only occasionally. It is a totally different experience from the intimacy of a one-on-one encounter. That said, I think it is something every hobbyist should experience at least once - after all, what is this thing of ours about if not about new experiences? And, like our hobby in general, it can be addictive.
Arrangements for threesomes will fall into one of three general categories: the prepackaged special, where an agency or an indie advertises a duo availability; the roll-your-own, where the hobbyist makes arrangements with two ladies separately to bring them together; and the referral, where the hobbyist broaches the subject with one provider and asks her to suggest or arrange a second lady.
It was nearly a year after I embarked on this lifestyle before I first crossed the bridge into having two women at once. I had often fantisized about it (that porn thang again!) but looked with trepidation on taking the step. When a prepackaged arrangement presented itself last summer, with two ladies who I had met previously and enjoyed being with, I figured what the heck. The advantage to the package deal for the MFF novice is that it is no more difficult to schedule than a normal appointment, and the inclusive donation is stated - one envelope covers everything, and will usually be less than the sum of the parts. The disadvantage, of course, is that there no choice - and such advertised specials are not always available.
The referral scenario is probably the most common. Asking a provider for a recommendation for a double will usually mean that both ladies know one another, have worked together before and are comfortable doing so. (This is, of course, a given in the prepackaged scenario.) Each provider will receive her own donation, and it will probably be at her usual rate, though not necessarily. But I must admit, I have never gone this particular route, jumping directly from first grade to third.
The most difficult to pull off successfully is the roll your own scenario, introducing two ladies who have not previously met - the most difficult, but certainly the most satisfying. Personally, I would not suggest this for a first timer, and would only do it with two providers who I have seen multiple times and know well, who am certain are both truly into bisexual experiences *, and where I have a reasonable basis for believing that each would enjoy the other's company. I have been told by ladies of client-arranged duos in which she felt quite uncomfortable with the other lady, for any number of reasons. And, of course, in this scenario, the donations are handled separately between you and each of the ladies. But another advantage to this type of arrangement is that it can be played out under some interesting role-play scenarios - the bar pick-up of a stranger in town, or one lady playing the escort arranged by you to fulfill a fantasy of your "girlfriend" - the possibilities are endless, but so are the risks of a bad experience. But when it works, it can be truly amazing! Ah, will Tuesday never come . . .
I hope these general thoughts have given you some helpful ideas - although I know I've not answered your specific questions. Be aware that a threesome is very different from a regular session, but can be a satisfying (and exhausting!) experience all around.
* Just a footnote FWIW. In the TER profile category Two Girl Action, I suspect that the number of providers whose profile states Yes - Really Bi exceeds the number whose profile states Yes - Not Really Into It. I also suspect that if the assessments in this category were truly accurate, those numbers would be reversed.
that the one on one experience is so much more intimate. And preferred for me. However, the threesome brings an excitement and carnal intensity IF the two girls are into it. I would NEVER line up two providers who haven't met if I were a hobbyist. I work with Gia Foxxx in Tampa and it's a evening beyond compare. We just sort of feed off each other and we never know just what is gonna happen. I'll never forget our first threesome and how she went crazy when I started to gush. It got even wilder at that point and there is a review about that one. Our gents are just about out of their minds. But, we've worked together enough now to know each other's strengths and when to let our guy enjoy the other girl. Also, when to let him sit back and watch the two of us. It's great fun and always a challenge to see how NUTS we can make our guy. My profile says I'm not really into it.That's not true. They only give you two choices, 1. that and 2. really bi. I'm neither. I've been in the swing scene for years and I just plain LOVE SEX. So, if another woman is in the program we have a blast. That doesn't mean I want to date her because I adore men and have to have that thing that only you gents have. Live and in the flesh. A strap just doesn't do quite the same for me.
So, trust your provider to supply you with just the right third party gal for your otherworldly experience. Every man should experience it ONCE in his lifetime, IMHO.
Naughtily yours,
Anneke
Taylor,
Come down to LI because I want to do a Ashley Taylor & Taylor James double. You did promise me that you would make a return visit, so that I could have my dream double.
Actually, babe, it would have been four. Ah well, next time . . . . . I'll think of something
Now thats what I'm talking about!
Ashley,Toni, Taylor and me.....Wow!
Even if I died right after that at least I can say I died
a very happy man. Talk about a once in a lifetime expierence
Now all I need to know is what I have to do to make this happen.