For situations like that, my choice would be to let them all hatch, raise them for a while, and then butcher a few for meat. (But if any seemed unhealthy after hatching, I would cull them at that time, rather than trying to raise unhealthy ones for any length of time.)Mostly because in my area is difficult to obtain these eggs, so they are purchased from online. It’s unlikely they will all hatch and everywhere I read tells me to incubate more than I need because of this. Selling the chicks will be quite difficult as demand is low in my location so I’d like to avoid that if possible.
This would increase the chances of having 4 healthy ducklings, and avoid the difficulty of selling them.
(If you already considered this idea and rejected it, then I apologize for bringing it up-- I didn't notice it anywhere in the thread.)