Yes, if you're using male condoms, you should expect to have to change them a lot, unless the duo partners are fluid bonded (and chances are they are NOT). Not changing condoms when switching from girl to girl is a super easy way to spread STIs.
Female condoms (also called internal condoms) are a GREAT solution to that "problem," and are readily available on websites like Amazon and Condom Depot. They are also non-latex, feel more like bareback, and one-size-fits-all. So many benefits! I'm moving to using female condoms almost exclusively (though of course I will always have other options on hand). Clients that have never tried them before rave about it afterwards. Lots of happy dudes!
Now, about duos.... The vast majority of sex workers I know are queer (be that bi, gay, or pan). I actually think it'd be interesting to do a study of the prevalence of alternative sexual orientations among sex workers... It's got to be at least 70%. I'm actually hard-pressed to think of anyone I know who ISN'T queer.
That being said, if you pick the right duo, it should be super duper fun! I'd recommend picking two ladies who are "established" duo partners - meaning, they advertise as such on their websites, and have met and fucked before and are friends. If you pick two random girls who are strangers to each other, the chemistry might be off.
I think threesomes are so hot!