What is the purpose of keeping a drake for you? Do you want to breed your ducks? Is there a drake who is friendlier to you or the flock?
I would keep one.
I've tried keeping two with more hens than you have and it's terrible. They compete and it's worse than 2x the mating, it's like 4x the action and the girls just suffer.
I have a 1/2 acre pond. Grew up hunting greenheads in timber. Always was a pretty sight seeing them come in cupped / commited. We enjoy cooking with the eggs also. I was wanting to keep one of the greenheads and the swede if possible bc he has a trump toupee’ . The khaki doesnt have that prety of a head more chocolate green. And the rouen is just a fat mallard. The welsh definitely are the prettier of the drakes. I raised then from chicks; wife brought them
Home anytine tsc had ducks when she worked therr
So the drakes are for show; but if one sits on eggs i never deny a hen babies.
I also have 3 muscovy hen / 1 Muscovy drake but they stay to themselves and dont interact at all with the others