For the most part they get their own room. That doesn't mean they don't end up sharing though. I know some crew who do bunk with each other. Then again it all depends on how the crews are set up. For the crew I know that do bunk together they do a majority of their long haul flights together so they know each other.

As for pilots and crew mingling. The pilots are more likely to mingle with the technical crew and the crew will mingle amongst themselves. As B747-437B mentions there are those crew who do prefer to stay in their room while the others are out.