Talking to them about waiting until marriage... is not the same as taking them to a Gyno appointment.
Girls, need to know, about their body, how to take care of it, and the medical aspects of it, and about diseases etc. And how birth control is not preventative against diseases etc. And how birth control is not 100% fool proof. And how... they are in control of their own body. Not a guy controlling it, or that their body is used in order to get a guy to love them.
Sure, having open communication with them is important.
But, it is not just telling them what you think or want them to do morally or philosophically, it is also about them being able to ask you.... ANY questions they have about their body... and about relationships etc.
Ask the Doctor's office, if both can be seen together.
And ask your girls, if they want to be together or not. They may want privacy.