They are cute! If you would post a picture of the mallard closer up, and maybe focused on the tail, I can give you a 75% accurate guess on the gender.
That's nice of you to rescue them! By neck quiver, do you mean they are bobbing their heads up and down? Bobbing means they want to mate. Fighting is pretty normal among drakes, they have to establish who is in charge. They may also be fighting over who gets to pair up with you, that's why they don't do it with your dad and boyfriend. If you could find a few female ducks for them (any breed will work), they would be very very happy. We would love to see pictures of them, and