Just different varieties (colors). If they came from a hatchery, that would explain the different combs. Its not uncommon to see them with single combs (or no feathers on their legs, no silkied feathers, missing toes, ECT).
Good luck with them!
**** I thought I was saving a couple of silkie hen's.... What the heck am I going to do with 3 roosters and no hen's?! Haha