English question

There is no relation between you and your daughter-in-law's parents, so there isn't a term for addressing them directly. To a third person, you can say they are your son's father-in-law / mother-in-law, or simply your son's inlaws, or the parents of your daughter-inlaw. Directly, you will adress them as Mr xxxx / Mrs xxxx. If they ask you to call them by their first names, or when they start calling you by your first name, then you can address them by their first names.

我推薦您一個非常不錯的英語學習網站，里面有很多非常不錯的學習資源：

http://www.grammarfree.com.tw/tw/

希望可以幫到你!

姻家奶奶Marriage paternal grandmother

姻家老爺marriage master

they do not have a specific term for 姻家老爺及姻家奶奶. In my opinion, just call their name is fine.

father in law=姻家老爺
mother in law=姻家奶奶

2010-04-14 09:50:12 補充：
but usual in English we usual call their name or father and mother