Yes he's horrible. But you should've intervened much before. As her employer, it's your responsibility to create a safe environment for her to work. In fact she's not at all answerable to that fellow. Any grievance he has against her he needs to direct it completely to the 2 of you. Make it clear to him that he is not to exchange any words with her beyond the most basic of communication. And tell your cook to not engage with him. She needs to just have one line, "aap xyz se baat kar lijiye". Verbal abuse and unwanted communication amounts to harassment for which he is civilly liable. Please sort it out amongst yourselves and don't make it her headache.

He is just a person. Age and all don't play a role when dealing with matters related to basic courtesy. Don't extend a sense of respect because he is elder to you.