Is there a problem with two people lighting from a chanukiah that has two Shamashes and 16 candles? Say, Shamash, 8 candles, Shamash, 8 candles, all on one structure?
וצריכין ליזהר שיתן כל אחד ואחד נרותיו במקום מיוחד, כדי שיהיה היכר כמה נרות מדליקין
or as Ohr Someach expresses the halacha:
If a number of people are lighting in one household they should make a slight separation between their menorahs so that there is no confusion to the observer as to the number of candles.
So there is a problem with two people lighting from a double chanukiah.