Now would be a good time to invoke the "No Fraternizing" rule (I think it's called article 16 in the military). I think that I would sit each one down in my office separately and say something along the lines of "There is something we need to discuss. It has been brought to my attention that you may be romantically involved with another employee here. This is not an acceptable situation in my office. Patient care is the reason you are employed here. I trust that you can assume a strictly professional relationship with each of the other employees, beginning now. You have a thirty days' probationary period, after which time, should this behavior continue, you will be let go." I can't think of any EEOC guidelines this would violate - but perhaps someone can think of a problem with saying this. (I have been accused of being "direct" before!)
If YOU, the physician, don't even feel comfortable interupting them, then I can't imagine that patients aren't noticing. Either directly or indirectly, patient care is being impacted.
Good luck. Let us know what you decide to do.