Ah, yes. About the cross. How exactly both of them could at once have the same thought to imitate being hurt?
Are they perhaps being hurt for real but then deny it for the priest's sake?
Or do they perhaps have telepathy not just to peek inside human minds, but also to exchange their own thoughts and to coordinate their own demonic actions of temptation? (Like two dolphins swimming in sync are in ultrasonic communion.)
Or are they perhaps not separate entities, but mere appendages of some higher demonic / satanic being and thus they “act as one” because that's what they are?