Marc's apartment is exactly what was stated. It's a studio with 2 beds. It was a little tight for my brother and I, but we didn't intend to spend much time in the room. But Paris is expensive and the room is reasonably priced. The main bed is on a lift, and you push it up to the ceiling to be able to use the room. The second bed is a futon. Both were comfortable.
Marc and Rumi were very communicative; I received a book's worth of stuff to do in the area from them. Mark gave us a gift of quite tasty cookies as we arrived and there were a few snacks in a basket on the table as well.
One thing to note is that the closest train line -- the RER C -- is usually closed in the city center for maintenance starting just after the 14th of July each year. There were other walkable metro stops, but getting around sometimes required a little more time.