Fit/skin clothes to a 3D character (3D modelling and skinning)

Design details: I have two 3D characters that are rigged and skinned, a male and female. I also have 2 sets of clothes (tops, bottoms and shoes) for each character, however these were modeled for different characters.

I therefore need these clothes to be sized and skinned to my characters so that they fit well and can be animated with my character. As the clothes will be interchangeable within my app it would be best to provide the clothes within the same character file.

Also, parts of the characters model's mesh should NOT be removed (which I know helps solve clipping issues), as further clothes may also be applied and made interchangeable.
Ideas for the visual style: See FBX files
Extra notes: Files are provided in FBX format.