Cute babies! I have a peacock,@ 60 guineas, 20 chickens, 8 muscovy and 11 different ducks....(I also have 3 just hatched from incubator muscovy babies(just today) and more eggs waiting to hatch)
anyway...I feel you have possibly 3 males by your pictures....didn't you say they were all close in age?(by days maybe?) if so, the muscovy male is much larger than the female and grows quickly in size...
by the pics it looks like 3 are much larger and those 3 appear to be close in size??? they are there with you...if I am right @ the sizes, then the bigger ones are boys...