I've had a couple of doubles, and they've been fantastic! So sometimes I go through my Favorite File, which doubles as my Wanna See File, and a couple of ladies look especially desirable and I start thinking, Wow! I'd like to have a couple, three hours with both of them!

...to get together for coffee and meet each other first before doing a double.  Even then there's no guarantee it will go well.  I know a provider who met another provider at a Meet & Greet.  They did a double and the provider I know said it was terrible because of the other provider.

...it would be good if they checked each other out beforehand. I guess I just took it for granted that they'd at least call one another.

If they are not advertising as a double, too many things can go wrong to ruin the session.  If you have money to burn, then go ahead and experiment.  Even though I have been known to TOFTT, I still want my money's worth, and the thought of putting two strangers together with me for the first time looks like a recipe for disaster, and potentially a giant waste of money that could be better spent somewhere else.  Thumbs down from my perspective.

I've done this before where a client had a regular provider he liked and wanted to bring me in to a session with the two of them. This client and I had seen each other a couple of times. I met with the other provider for a drink before doing a doubles session we had, we got along great, and had a very nice time together. Since then we've done a few doubles sessions together. It's always ideal when everyone has met! Best of luck!

risky is always exciting, and in this case, hot as well.  Just go for it!

really fake because the two providers are not comfortable with each other.  Another possibility is they get competitive, trying to make the other look bad, so you will repeat with just one of them.  

Contact one, and give her the info on the other and express why I think the two of them together would be exciting, what I liked about the 2nd provider, and then ask if she had any friends that were similar who she could invite to join us.

I guess I knew that when you see the 2-girl Q marked "Yes. Really Bi." It doesn't necessarily mean that they "Really" are bi.

I'd reach out to one of them, outline what I had in mind in general terms and see how she responds. Who knows, they may already know each other and just don't advertise it. You'll never know unless you ask.  

To discover if they know each other, or would be willing to consider a double with each other? I had an email from a client asking this question and the other lady and I then started emailing each other to see if we liked the sound of each other and then met for coffee and agreed to the booking and it was great fun! I also then made a friend from it in the industry and the client had a brilliant time - so he said

behind closed doors...  if they are both agreeable, they'd likely want to meet in advance.

before actually playing together is kinda important to some of us.

What if one doesn't show, or shows up 2 hours later than planned, or is on their period at the time....if you don't have any existing relationship with both, this could go sideways very very easily.

hobbyist to have seen at least 1 of the providers for a one on one and be sure the two providers are comfortable with each other. From experience, if the providers are comfortable with each other, the session will be much hotter for all.

That actually is the only way I do doubles. If the client has the lady already selected, and he coordinates and schedules the date with the other provider on his own. Just tell both ladies what you are thinking and pick a date and time that they both are available for. Ask permission to each provider if you can give the other providers info over. I don't see anything to worry about!