We know, as a FACT, that many of the couples know each other.
Lina & Mark and Maya & Stephen are friends, and L&M probably recruited them after Elena & Arthur left. Same apartment complex. Alma & Stefan introduced their friends, Isabella & Marcello, to their apartment. A substantiated rumor suggests that Leora & Paul got their apartment via Lina & Mark, via a family connection. Nora & Kiko had many friends and visitors; never once did the other Barcelona couples appear.
At one time, either Manelet (?) or Corboblanc (?) produced an advertisement written in Spanish advertising this RLC apartment opportunity in Barcelona.
None of this necessarily proves chillifingers' assertion. Nor does it disprove it.
But then, Truth has no monopoly on CamCaps. It shares this site with smoke & mirrors, and the fog of war.
http://philosophy.about.com/od/Philosophical-Theories-Ideas/a/What-We-Cant-Know.htm