Just wrapped up a 4 day stay at Francois apartment is the Monmarte section of Paris. The apartments worked out quite well for our large family, where my in laws could be in one apartment while myself, wife and children stayed in another just a few feet away.
The apartment building was very easy to find, and Francois was excellent and timely in his communications.
Coming from the CDG airport with a group of 6 people and luggage via the metro system was pretty easy and straightforward. About 35 minutes. The Abesse or Blanche stations are your best option, as Francois pointed out. The apartment is a 5 minute walk from either station.
I found the apartments to have everything we needed, and best of all they are quiet even though you can walk a short distance and be in a lively area.
Commuting to any of the main sights in Paris was easy given the proximity to the metros, and the Sacre Coeur is a pleasant walk from the apartment. In the neighborhood you can find many shops of food, wines, cheeses, cafes. I had no issues walking anywhere at any hour.
For a stay in Paris I suggest you give Francois's apartment a try. If I return to Paris again I certainly will