How do you make sure Gemini with Nano Banana does what you want it to do?

Nano Banana overall is great and alot of times it does what I want, but there is still so many times it doesn't do what I want at all, and I don't get it.

For example I had a photo of two people doing something on an image… and I uploaded it.
Then I uploaded a 2nd photo of two different people alltogether in a different scene.

And my instructions were clear.

Replace the two people in the 1st photo with the people from the 2nd photo. Keep the background the same, and the poses the same and the overall scene the same, I just want you to put the two people from the 2nd photo to replace the two people in the 1st photo.

How much more clear can I be?

Result is anything from not doing ANYTHING at all, and just giving me the same image, to putting those two people NEXT to the two people in the image… to replacing the people but in a pose from the 2nd photo… like I don't get it, my instructions were clear were they not?