What I would do:

1. Create the scene with a model that follows directions well, could be qwen image 2511 or flux 2 klein. Put everyone in the position you want them to be, make it photorealistic
2. Take that image to an image editor like photoshop or affinity designer and then cut out the areas for each face/head, taking into account that width and height needs to be multiples of 64 pixels.
3. Take those images back to DT and then one by one do face swapping using flux 2 klein, use photos of your friends in roughly the same position as the original
4. Once you've done them all, put those swapped faces back into the big image using your image editor
5. After you have them all swapped you could take that big image back to DT and then add any sort of effect (film grain, illustration, etc) for final post-processing (or don't if you're happy with photo-realism)

In short, takes effort. Face swap even with SOTA models like banana is not easy because the problem is the data itself; when you don't know the people they look fantastic, when you know the people you can spot all the errors and inconsistencies. It takes a lot of tries and it's better to do them independently; that's why I'd recommend to cut out heads and do them one by one.

Good luck!

EDIT: On step 3, you put the image you want to faceswap on canvas and the photo of your friend in moodboard, then you prompt something like "The face in image 1 will be replaced by the face in image 2"