Three of them are doing just fine. However, one of them has a problem as evidenced by the leaves which look as if someone has held a candle too close to the edges of each leaf and they have become brown and crispy - covering almost half of the leaf, but starting with the outside edge (away from the stem).
Again infants and children normally drool during sleep, but some adults too drool during sleep. Moreover, drooling in case of adult is not always normal. Drooling can be quite common in adult while sleeping. But when awake, drooling in adult can not only be embarrassing but very uncomfortable leading to social and mental burden. The reasons for an adult to drool during sleep can be due to an open mouth, abnormal structure of the mouth like enlarged tonsils, large tongue or overcrowded teeth.
Pain and nausea can cause your cat to drool so it can be an indication of problems elsewhere in the body and can also indicate exposure to toxins or caustic chemicals. Refusal to eat is another sign that the drooling is a sign of something more serious.