In Spain, double means for two people, triple for three, etc. Ask about the specific configuration of the beds, because quad could mean a double bed and two singles, two double beds, or four singles.

Rooms in inexpensive hotels tend to be small, unless they are in the country. Hide a beds aren't common, unless it's a suite. If you are spending more than a day or two somewhere, you might look into apartment or house rentals, sometimes this is cheaper than a big hotel room.