Is it correct to say you are going to take dinner?
Yes.
No, it is not. Usually, you say you are going to "have" dinner,
or "eat" dinner.
eg. I am going to have dinner at 8 o'clock tonight. You are
going to eat dinner, even if you are sick.
To "take" dinner brings up the image of one "taking," or
"stealing," someone else's dinner.
Hope this helps !