hey Kawakibi.
easy staff really.
you should shoot them on a green screen, (both of them), and then you can change their background by keying to whatever you want. split screen or not….
make sure each image get the right colour correction and lighting as the bkg she is on, and when they merge, animate the values to the new BKG.
best result will probably be if one character move in to the other character’s word.. but that’s up to your copy/creativ/script I guess.
good luck!
Ido Shor.