Mar's place was excellent for our large group. We had two families of 4 - 4 adults, 3 kids under 10 and one infant. All of us were comfortable. The pack-n-play for the baby was great (it was longer than the standard US versions), plus a little high chair for meal times and even a baby bathtub that we were not expecting but came in very handy. I also found a bedrail to contain a toddler to one of the twin beds so definitely consider this place if you have small children. The master bedroom that has the infant bed in it is next to the street. I had brought our white noise machine and we used it with success.
Centrally located to so much, easy to take public transport, and a large grocery store across the corner. The dryer stopped working while we were there and Mar generously - and quickly - offered us a solution at her expense. Overall a great place to stay with a big group in Barcelona.