Do you have guineas, ducklings and chicks all together? Are all about a week old and how long out of that week have you had them. Were some shipped to you or did you buy them from someone else. How long have you been feeding them sugar water? I'm trying to help but I'm having a hard time following just exactly what is going on. Did the chicks and guineas that died also have diarreah prior to death? Any other symptoms? Were they lethargic at all.
Ducklings do have the runniest, stinkiest poop on the face of the planet so I'm not sure if what you are calling diarreah is actually diarreah.
In any event, stop all sugar water. Add some vitamins and give them some high protein food to eat, like scrambled egg, shredded cheese, or wet some dry cat food and mush it up. Something to get nutricious food in their little bellies.