Since you're not sure if they came from the same tank, it's probably best to acclimate them separately. This is strictly from a water chemistry perspective.
I would let introduction happen in the tank once they're more comfortable. I have two anemone crabs (Neopetrolisthes ohshimai) that don't mind each other. One is smaller than the other, and I don't know if one is male and one is female, but they freely roam between the 7 carpet anemones in my tank.