Ours have met each other once, when we'd been together 10 years! (We're not married so no wedding for them to meet at) It was polite and everyone got on OK, but although they live much nearer to each other than they do to us, I don't think they're going to see each other voluntarily or be mates.
They are very alike though, our mums especially are extremely similar. When we had them all meet up it was in a big city to go to a restaurant for lunch... everyone got lost, everyone flapped, everyone couldn't find their way back to the car park - it was like herding cats.