First things first. As far as I know, squatters as they exist now got started in the late '60s in hippie liberated places like Copenhagen, Amsterdam, London, and West Berlin. What they did was move into unoccupied houses and apartments and live there for free. After the hippie thing died out a few squatters hung on, and they showed up in Barcelona in the early '90s. That is, long after Franco was dead.
Those who hung on were not the flower-power types, who were all nice and middle-class and by about '71 were social workers or teaching el-ed. They were street people, and they still are. They may claim to know something about politics, and a few of them actually may, but basically they're nihilists and extreme hedonists. Dionysians, if you will. They proclaim they are anarchists and certainly act like they have the right to destroy whatever they want.
There are something like 20-35 squats in and around Barcelona, each one with 5-10 people living in it and a larger group of hangers-on. The real squatters are hardcore leftist radicals, dedicated to the overthrow of everything by every means possible. They look and act like your standard punks. They are generally streetwise and individually out for their own interest--they live off the hangers-on and their contributions, and are very careful about not sharing any of their own stuff.
The hangers-on are middle-class college kids who will mostly get slightly smarter in a couple of years and get nice middle-class jobs at La Caixa but pretend they're still radical and do dumbass things like vote for Esquerra or Iniciativa. They generally don't know they're being used by these hardcore squatters, and they actually think they believe the nihilist anarchist rhetoric. If a middle-class college kid spends more than about three years with these guys he's likely to join up with them and not get out for years.
Here in Barcelona the squatters are loosely organized. There are a couple of what they call collectives that claim to have representation from the various squats and to be in a position to negotiate with city authorities and the like. They do have access to lawyers, we know that, and are more than happy to use the loopholes in the law to save themselves punishment. A strategy they use is--since they can't be kicked out without a judicial order, and the owner of the property has to file a brief with the court to get said order--is for the lawyers to look through the property register for places that have a lien on them so that there's no legal owner who can go to court. Catch-22.