If it is botulism- they are getting into something spoiled- it may be that only the affected bird(s) know where the tasty treat is, and the others don't. Or the affected birds like the item better- and they are getting enough of the toxin to have symptoms. Dead animal- maggots ect are usually the culprit in land birds. Any dead things around, compost with animal protein, maggots ect? Improperly canned food is usually the culprit in people. Walk the grounds, look under coops, ect. Question the family on what they are feeding the birds. I would NOT give any animal that is ill epsom salts- you will likely just dehydrate them, possibly hasten their death if they have a lethal dose of the toxin. Careful force feeding of food/water is fine, or even medical grade charcoal if you have access to this. For mild cases where the animal is still walking around with a droopy neck- you need to support them through it (food, water, warmth), and prevent it from happening again- by finding the source.