Scene: Sally and Gillian and the aunts are sitting around the table getting drunk. Eventually they realize they're drinking from Jimmy's ghostly bottle of tequila, "Someone left it on the porch", etc.
Jimmy's tequila was spiked with belladonna, enough to kill him. Wouldn't the four of them be affected as well?
I wondered about this myself, but I started thinking about how much was consumed. Jimmy Angelov would have consumed a large amount on his own while the Belladonna was still not fully absorbed into the alcohol. The women were passing the bottle around amongst the four of them... granted that their Margarita's were probably made with the same bottle of tequila. When you look at how much of the bottle they consumed, it isn't likely that they really had that much when split between the four of them. Also, the women had probably gained a tolerance to the Belladonna. Jimmy had only recently been introduced to its effects. The women had been using it for years.