Translation:Grandfather and grandmother do not come to our house.
To further my understanding of the sentence, I have a follow-up question. In previous lessons, को was taught as "to". Would "नाना और नानी हमारे घर को नहीं आते।" be correct, too? Would there be a difference, say, with पर saying they come INTO the house proper, whereas को saying they come TO (near) the house, but not necessarily INSIDE?