"Let's go and have lunch together!"
If you say that to a Chinese, he/she will know what you are talking about. But they won't say it in that way, or I mean it's not native.
The structure of Chinese and English is difference. In English, we can say "Let's go and have lunch together!" but in Chinese we won't say "我们去吃午饭一起吧？", we will say "我們去一起吃午飯吧"/ "我們一起去吃午飯吧".