YOU SAID:
Let's have grandma over for dinner.
INTO JAPANESE
おばあちゃんに夕食を食べに行こう。
BACK INTO ENGLISH
Let's go eat dinner with grandma.
INTO JAPANESE
おばあちゃんと夕食を食べに行きましょう。
BACK INTO ENGLISH
Let's go eat dinner with grandma.
That didn't even make that much sense in English.