I totally agree with Miss Lydia about your little flock being good therapy once you've sorted out who to keep. When everyone is getting along peaceably, it's so nice to just sit and watch them. I'm doing that right now, my ducks are happily eating snow right outside the window and I like just watching them be happy.
It won't matter which two you rehome, I would keep the ones you like best or maybe even give your coworker a choice between two if you really can't decide. I like how you describe Bopper because I have a loudmouth duck and it always makes me laugh, hearing her shout her head off. Anyway, I rescued five Indian Runner ducks when they were a few months old, they'd been together their whole lives. I have other ducks too, but the Indian Runners always stayed together in a little group. After having them for a year, the two drakes started getting too aggressive with the girls, so I had to get rid of one drake. I didn't want him to go alone, so I picked a girl to go with him. Like you, I tried to figure out which girl got along best with him, but in the end, I just picked the most skittish one (they were going to a hobby farmer who enjoyed having ducks on his property, but didn't treat them like pets like I do). The remaining three were fine. They were maybe a bit confused at first because I got rid of the dominant drake who led the flock, but they just decided to join up with the other ducks instead of being their own little separate flock. I felt really bad splitting up the Runners at first, since they'd always been together, but it's so so nice to have a peaceful flock again.
I hope your husband feels better soon, I'll pray for him and you if you don't find that offensive.