How to sex muscovy ducks

Much of what I have read (almost all) in regard to sexing muscovies does so by comparison (female to male). What if you only have 2 same age (siblings) and they seem very close in their development? Obviously I might have 2 drakes but it is impossible at 13 weeks to tell for certain. The obvious drake husses all the time and acts aggressively toward me. The other is silent and less emotional and more trusting. The slightly smaller one also does not fan the tail as much as the drake who walks around with it out much of the time. The slightly smaller one is more active and a better hunter but I assumed that is because the bigger one might be bogged down with more weight. That said the drake has flown along the ground already but it is clear they are both preparing for flight.
Your muscovies look identical to mine in color! How old are they in this pic?

Example pictures would be helpful. If you add pictures I will re-rate this.

The verbal descriptions are good, but hard to follow without photos.

Next time you raise ducklings please take photos for all these stages and add them. When you do I'll raise my rating.

short and to the point. pictures or a reference to some pictures would help the reader understand the subtleties.