They were both with the sisters at the same time! They were super naughty and very erotic! Not something I discuss often because of the taboo nature of the activities. I have also been with best friends before but they did not have any sexual contact with each other at all but the sister's did!
I have recently seen gangbang videos with two sexy Russian sisters by legalporno where they play with each other first and with toys, then get gangbanged by a hand full of guys.