An advantage of 3-somes with whores is that, if they don't have to do their no-no's, they couldn't give a damn. But if you want the women to 'get into it' as it were, it can be lots to negotiate. Make sure you have a big bed for a start. I had one awkward DP MMF threesome where the other chap got his foot stuck at the back of a radiator. It's a lot of arms and legs about the place and unless you want to be very vanilla it can get complicated!! Even if the prossies say they like working together, another another problem can be 'jealousy' which is really just her being an attention-whore (two ho's in one haha - nah not really - no pun really intended).
Most whores either want to be the centre of attention or just do what is expected to get paid. Start treating one as a bit 'special' and the other's peformace sometimes slackens. A way round this is to treat it as purely PSE if that's your thing . . . PSE can be generally pretty emotionless and still brilliant fun - like athletics. It's a lot easier to negotiate than a pretence of being touchy-sweetie-I-fluffie-like-you-dearie or 3-way GFE.
If it is really 3-way GFE, I find it is always best to let the women bond sexually first and then join in. That way, there's a ready made scene and you just add to it and enlarge it. If you start off with one, make sure the other one has clear instructions before you start is my advice. There is nothing more cock-deflating than coming down to earth mid-stroke cos some brainless ho is not doing what you want her to do and requires it spelt out again a-b-c.
Beginners are crap. You need at least one person in a threesome who has a clear idea of what they're doing. If she's reading this, the ex-LMP girl who's on this forum, from my personal experience, is someone who is good at seeing the 'big picture' for instance while performing.