Hi Nadia,

Tooth/gum problems can cause drooling, so you'll want the vet to check
her/their mouths carefully. It seems odd to me that both of them are
drooling, though. It's possible that Sweety's was just a one-time
occurance, or perhaps she was overzealous about grooming?

Some cats, as they get older, will drool when they are very happy or
content, sometimes when you're petting them.

Rene