It was very common in WWI for groups of men from say a village, even a street, a place of work: colliery, railroad workers, to volunteer together and be allowed to fight together. It was good for morale I suppose. There is a term for these units, something akin to "Mates Brigades"; however, that is not the correct term I'm sure. I don't know if it happened in WWII, but I can't see why not. Someone with more knowledge should be along soon.