Shirako;
Not entirely sure on your posted question, but here goes.
To strip the paint use an Oven Cleaner Spray (Easy-Off). Place the cars in a sealable container or plastic bag and coat with the oven cleaner. Leave them overnight sealed in the bag and you should be able to simply rinse the paint off with running water and a slight scrub with an old toothbrush.
To remove the body from the chassis...Try stripping the paint first, the reason I say this is I do not know what type of glue/adhesive was used to build these originally. Sometimes old glue will simply "pop" apart with a slight prying at the seam/joint, depending on the age and type of glue/adhesive used.
If you could provide some more details, I can possibly advise you further.
Cheers;
Gregory