Basically, as long as the customer knows what he's getting for the price you can charge anything you like. If the customer believes the price is too high then the customer need not buy.
Generally, the more you buy the cheaper per item. Buy one pair of shoes get 50% on the second pair. Lol
I'd be happy if prices were based on work rate and house costs.
If 2/2 meant that just as much effort was required for each lady as 1/1 would then ideally it would mean that each lady should get the same and perhaps the house slightly less since only one room was used.
In a 2/1 situation I would assume that it would be easier work (getting more buck for bang) so ideally would mean less than double because ladies work less and house uses less supplies.
If 2/2 and swapping generates more work or even stress/anxiety then more should be charged.
I don't speak from experience as I have not had a 2/2 experience and very much doubt I ever will.
It's just maths to me.
Ultimately, the arrangement and pricing should between you WLs and your client(s) and probably differ based individual clients too.
Most important is for everyone to know where she/he stands before entering the room.
I'm always in favour on the WLs getting a bigger slice of the cake.