Gidday

Yes, I vote you get more ducklings. The breed possibly doesn't matter particularly - unless ducks are fussy about being with the "right" breed. Are they? Do they even know?
I think the risks of having fights is too high to overlook - it would be really unhappy to have more lonely Berts, or Svens. And yes, it could be a bit of a drag to have to do the first 8 weeks again - and it might be getting a bit cooler? but I think it is a good idea.

But think of what has happened with the first group. Of all of them - you have been left with one, Bert. Is this telling us that ducks have a slender hold on life? What is their average life expectancy?

What would you do with 15 ducks? Get their eggs & sell them? You could get some quails & sell their eggs too - I don't suppose you remember it, but I did some hardboiled quails eggs for your wedding. They tasted a bit different from hens eggs.

Good luck anyway! I look forward to following the next lot online.