help with photomontage with Disney characters

Are you hoping to do this with Ai or manually?

If AI then start with an image with several people.

Select all (Ctrl A)

Click on Generate in the Contextual Task Bar

Select the Nano Banana model and use a prompt like

Replace the person on the left with a cartoon character of Snow White

It may work or it might not.  

Flux Kontext is reluctant to render copyright logos, and that might also apply to copyright figures.

If you want to do it manually, the issue is going to be perspective.  That means finding a cartoon viewed from exactly the right angle etc to fit the scene.  So I would start with what I couldn't control, that being the cartoon characters.  I would then try and take a photograph that those characters fitted into.

Do you know about Select Subject and its 'People' mode?

Select a person

Expand the selection a couple of pixels

Use Generitive Fill to remove that person.

The way I composite is to copy areas I want the new element behind, and place those layers above the new element.

I used Select subject > People again to help me in this.

When I have the new character in place and sized etc. I'll click onm Harmonize in the Contextual Task Bar which will match lighting shadows etc to the rest of the scene

Does that help at all?  There are dozzens of tutorials on compositing with Photoshop, and a good few already on using the new Ai tools.  The latter will use Generative Credits, and I am guessing that you do not have heaps of them?

I'm attaching the final result I'd like to achieve.