You can beware of the intruders and thereby beat them at their first punches. Simply continue to look into the original talker's face, not permitting your gaze to slide away into the intruder's eyes. The interrupter usually gets the message in quick order. Please don't try that again. It's not nice.
Some partners discover early that one talks more than the other.
Perhaps one talks too MUCH more than the other. When that occurs, it can be a bit overbalanced and that off-tilt can lead to an individual's lack of attention, or artificial listening while thinking about other things. In other words, one individual may simply come to tolerate the constant haranguing of the other. That is not truly communicating, obviously. It is merely putting up with annoying sounds.