First, Second, and Third Pictures are Females and the Fourth is a Male.
The bird in the second picture looks to me as if she may have scaly mites -- have you had her checked by an Avian Vet? If one of your birds have mites then all of them will need to be treated.
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Budgies aren't always that strict about gender.. I have two males that insist they're a couple, too ("Juana", who is very clearly male in spite of the name, and Colborne, who is also very clearly male).
Ignore me if you have already had it checked out or are treating the bird already, but you might want to do something about the green one's beak. The picture is not 100% clear but that looks a bit like mites to me.