Yeah, you have been to Germany and still speaks broken German. Weird, ey?
Dumm means dumb. The German word for idiot is the same as in English as it's a Latin word. You don't adress a person in singular and in plural in the same sentence. need to polish your English gramma, too.
In German, the word Schwein (swine in English) is usually not used to describe someone as stupic. Pigs are synonyme for dirty (in the sense of dirty sex, kinky sex) but also f
or someone who is just dirty in all aspects.
If you want to insult a female as stupid, you would use cow, goose, or turkey, like stupid cow (dumme Kuh). For guys it's usually more vulgar like dummes Arschloch, dummer Wichser, Penner (arsehole, wanker, bum).
Another lesson for my vietnamese German expert.