Ginny would either be ecstatic and hole her with filthy questions about what Draco was hiding underneath those ridiculously well-tailored suits or she would give her the silent treatment while she came to terms with the relationship. Arthur would probably be the most accepting, although the thought of becoming somewhat closely aquatinted with Lucius Malfoy and sharing a grandchild with him - because Arthur was for all intents and purposes like a second father to her-, might be enough to send him into a state of temporary shock.