Texture painting on an object also adds paint on the back of another As you can see from the gif below, while trying to paint the shoulders object some paint also reaches the back of the character model, which is a separate object. Both objects have separate materials and textures.

https://imgur.com/a/hrwxnLG

Blend file:

http://www.mediafire.com/file/la5qv22pnbmb28h/male_character_2.blend/file

(sorry, I couldn't get blend-exchange to work)
You have your texture paint slots set to Single Image mode, so the only image that corresponds to paint is the base body image. The palderons image texture is solid brown, and if you change to Material mode then you can paint to the separate texture images.