To each their own but as mentioned elsewhere guys tend to have a "refractory period"....
Two ladies interacting tends to greatly shorten that timeframe.....
The biggest complaint I hear from guys is that occasionally the gals get so into each other that they forget he's around....
That's no fun.....
I can't imagine during my time with two ladies there not being considerable interaction between ALL parties......
Doing a gal in doggie while she is DATY of the other lady and eye contact with that other lady is quite the mental image!