How do I stop the aggression of my ducks

I have 2 Aylsebury ducks, 1 is getting over a leg injury and has been doing well, but recently i've gained 2 new ducks 1 kakki Campbell and 1 buff orpington. They were fine the first 3 days, the injured Aylesbury, Jamima, stayed in the pond so the fact that she is weeker and perhaps vulnerable didn't notice, now they've started to pick on her how can i stop this, should i get rid of the new ones ? i don't want it to affect Jamima's recovery. Also the new ones keep bobbing there heads up and down to the side and making a horrible weird quacking noise does any know what this means, i can't seem to find any information on understanding a ducks behaviour, any suggestion welcome, tips, links, perhaps if i understood there behaviour more i wouldn't need to worry so much. PLEASE HELP SOMEONE..

LOL oh my!!

Well first I have tons of duck experience. and we have 2 mallrds of our own.

You do not say what the sexes are of your babies?

Head bobbing can mean a few things. but often its a male looking to have a female.

It can also be a sign of aggression towards another duck a kind of . HEY you . do you see meee I mean business!

NOW. your problem is normal. You see even domestic ducks are instinctive.. and in the wild. ducks in a flock will isolate and turn on an injured duck because an injured or sick bird can draw in predators to the entire flock you see.

This is all your ducks are doing.. they are not being malicious they are just being ducks.