They are either ferals or Rollers I think.
As to sexing, if they are older and had babies already you should be able to tell by the pubic bone. You pick up the bird and feel for the 2 pointy bones by the vent, if the tips of those 2 bones are touching you have a male and if you have about a finger width of space inbetween the tips of those bone then its a hen.
The pubic bones of a young hen that hasn't laid an egg yet will be closer together though and can be mistaken for a male.
Another thing to look for is behaviour, do they squabble a lot? - That would mean most likely 2 males. Or does one coo lots in front of the other but the other seems indifferent? -Good chance you have a pair.
If they start nesting and you get 2 eggs in the nest, that means you have a pair. If the have 4 eggs in the nest it means you have 2 hens.
Thats all I can come up with right now, I bet other pigeon folks will chime in too.
Anna