I just beat the Elite Four yesterday. I went to Lumoise station, got the pass, and went to the city.
I entered the Battle Maison, battled like 14 times and the 3 girls never showed up. (The owners) I tried going through the door, and it didn't work. I tried triple battles too.
How do you battle the 3 girls?
The girls battle you at the 20th Match of your win streak in the different battle modes. After this you unlock the super mode, in which they will appear after a 50-win streak(source serebii)
You must win 20 consectutive battles then the chantelaine will show up I won 15 battles, and then lost.
The first time you face the girls is at battle 20 the second time is during the super battles at 50. Below I posted a link that contains a lot of information about the battle mansion that I can say 100% sure is true. After battle 50 I am unsure if you face them again.... http://www.serebii.net/xy/battlemaison.shtml
