The epsom salt flush is much more strong in clearing the digestive system of the poison than molasses flush. Both will give diarrhea and will dehydrate some, but epsom salt is more severe, but more effective if you think it is botulism. I would look around the ranging area for any dead animals...
I would be suspecting either botulism or moldy feed, since 2 have been struck at once. Botulism is caused by eating a toxin contained in decaying animals or vegetation, fish or maggots from any of those. It can kill in 12-24 hours, but if a chicken lives 48 hours, they will probably survive...